Probably mostly scummvm fixes and optimization as you can see by this news http://scummvm.org/news/20180629/
The scummvm version in the release is indeed a custom one.
Seems also that more languages has been added to Riven.

Would have been better if they had provided a changelog given they know they would release all the collection today.

Sphinx and the Cursed Mummy has been updated.

Changelog for Patch 2018-06-28 (29 June 2018)

Made the fan-favorite intro logo thunderous again. The sound was broken on release due to a little hashcode header mismatch.
Add initial support for the mouse-controlled camera that we have been teasing for a while, we still need to add a mouse sensitivity control. The player can shoot with the left mouse button and exit first-person mode via right-click. The groundwork for keyboard action mapping is laid out and it will probably come after this.
Save the vertical sync changes to Sphinx.ini, fixes disabling v-sync in the in-game options.
Prefix the screen name with a number in the graphics options, useful to distinguish them in case there are two or more screens with the same name.

Add support for clicking the "(B) Back" labels in the pause and main menus, now the user can go back and cancel via mouse.
Carefully hex-edit the level data to improve draw distances of NPCs and triggers in the Abydos Canals. Now characters like the the boat owner, the Mad Boy/Juggler and the giggling lady in the Main Plaza can be seen from afar.
Add several much needed HQ textures for the Abydos Museum, refurbish some wall textures to add some lost detail. Make some signs and canopies partially transparent via alpha-testing/alpha-to-coverage.
Remove the squarish/invisible roadblocks in the middle of the ramp in the Great Wall Entrance II Room, the collision meshes of the wooden pillars poked through the ramp they support. This is a long standing bug still present in all the original console versions.

Fix the hanging flags collision in the sneak corridor of the Castle of Uruk during the second mummy visit. Now the mummy doesn't get stuck and can walk and sneak under them, hopefully without introducing some extra regressions.
If we skipped a cutscene with the inventory key and the dialog/help window was in a pause point waiting for user input we would get stuck in the fade-to-black transition after skipping it, and we would also need to press 'accept' to return to normal gameplay. Fix that so that pressing the inventory/skip button suffices.
Reimplement some beta features and mechanics asked by modders:
Add support for the PushFlag_AmunRa flag in the XTrigger_Pickupable and XTrigger_Pushable triggers; it was halfplemented. Set the needed strength to 2 if we have the Hands of Amun + Hands of Amun Ra or 1 of each. Previously it only counted the amount of HT_Item_Ability_HandsOfAmun, and there was no reference to HT_Item_Ability_HandsOfAmunRa.
Whitelist HT_Item_Pickup_FireDart for pickup creation, which is also used while dropping items randomly in breakable containers. Also, add support for dropping fire darts on intelligent item generation.
Now when ContainerFlag_SpawnPickup is checked in EuroLand the FireDart flag can generate an item in either random or intelligent mode. The behavior in the final game shouldn't change because this item isn't flagged in any container, only in beta maps.
Fix the slightly offset highlight tab in the Notes section of the Book of Sphinx; the currently selected objective/entry text overflowed a bit.
Update the copyright year of the boot-up/legal screen from the initial 2017 to 2018.
Use the HQ selection tab texture for the Book of Sphinx again, it regressed after the latest changes.
Losslessly compress all of the HQ texture replacements, reducing their disk footprint and halving loading times.
Reduce HQ texture replacement micro-stutter during gameplay.
Add some framebuffer discard optimizations on MSAA resolve.

There's also Patch 2018-05-28 that was released here today:

Thanks. I missed that one.

War for the Overworld

Patch 2.0.2 "Sufficiently Surveyed Surfaces" (29 June 2018)

Gameplay / Balance Changes

Units

Augre

Now slightly less likely to use the Foundry and slightly more likely to use the Garrison Juggernaut

Now slightly less likely to use the Foundry and slightly more likely to use the Garrison Priestess

Updated needs to match the Cutlist Spirit Worker (Permanent)
Movement speed reduced by 10%
Work speed reduced by 25%

These changes do not affect Spirit Workers created by the Spirit Worker potion Wizard
Updated needs to match the Witch Doctor

Spells

Volcanic Bridge

Mana cost reduced from 100 to 50

Underlord AI Changes

Underlord AIs can now make use of the Besiege ritual to attack enemy Dungeons
Sloth focussed AIs will now be able to make use of the Infernal Urn to transform Brimstone into Quartz
The AI can now use Hellfire potions
Added 7 New Build Orders
Adjusted a number of existing Build Orders

The Medium Difficulty AI has received a number of tweaks

Now has the ability to drop units near rally flags

The rate at which it can pick up and drop units has been reduced

The rate at which is is allowed to spend sins has been reduced
It will now be slightly more aggressive
The AI will now trigger Sentinels more intelligently
The Master AI is now able to use defence parts to heal existing defences
The AI will now make more intelligent use of Work-A-Lot potions
When using Overcharge the AI will now wait until its Mana is exhausted
before triggering the ritual
The AI is now able to more accurately predict if it needs to return its forces to defend its Dungeon Core
Further optimised the behaviour of the AI on master difficulty
AIs will now hesitate less whilst attacking and will execute their plans more aggressively if they are confident of victory
Bankrupt AIs now wait longer before selling rooms

Level / Campaign Changes

The Under Games

Underlord Shale

Beast spawn rate reduced from 666% to 444%
Defence gold & mana cost increased from 150% to 200%

Visual Improvements

New Animations

Democorn - Receive Pay

Baby Democorn - Receive Pay
Arcane Chunder - Sanctuary work
Visual Tweaks to the Foundry Floor
Improved the possession view of the Firebreather
Adjusted the viewpoint position of the Behemoth in possession

Localisation & UI

European and Chinese localisations now in game for various text edits that were done for 2.0 and 2.0.1:

Various user-interface text improvements, including tooltips and campaign map names
Pre-2.0 Skirmish maps have had their creators' names added to the end of their descriptions
Fixed various old text style issues such as asterisks being used to show sound effects in subtitles
Lord of the Land unit subtitles (for future use in the Mighty Script Editor) have been tweaked to match chosen audio takes
New Mendechaus voice-over (for future use in the Mighty Script Editor) has had unique text keys added for each unique audio take being used

Miscellaneous Improvements

Debug logs which are generated upon game crashes are now fully GDPR compliant

Bug Fixes

Crashes & Gamebreakers

Fixed a rare issue that prevented some players from opening the Under Games if they had not completed the War for the Overworld campaign

Units

Fixed an issue that would cause units to attempt to walk out of prisons and arenas

Defences

Alchemines should now always load in with their potions after loading a save game

Visual Fixes

Units are now react to the visual height of shrine floors (such as the siege shrine) and can walk on the surface without clipping

AI Fixes

Underlord AI's will no longer ignore the last item in their build order
Fixed an issue where the Underlord AI would not use the Wisdom Juice potion on Vampires
Fixed an issue where the Underlord AI would issue an attack without removing units from it's Peaceband, meaning sometimes attacks were not correctly planned and did not meet AI expectations
Fixed an issue where Workers were not correctly receiving new tasks and thus would revert to older tasks such as nearby reinforce wall tasks over newer claim tile tasks
Fixed an issue where the Underlord AI would be unable to determine an appropriate attack vector on large maps where the enemy is well fortified and defended

Map Editor - General

The Empire Theme selector can now correctly select any theme, even if it is locked

Levels / Campaigns

Fixed an issue where the cutscene which plays after Mandalf is turned to gold in Heart of Gold level 1 could be disrupted if he was mined by workers during the cutscene, preventing the level from ending
Fixed an issue where the VFX on the objective forge on Heart of Gold level 3 would not play correctly
Capturing Pre-Placed rooms in the "Seastead II" skirmish level will now correctly allow units to work in them

Localisation

Fixed an issue where Chinese fonts were not displaying correctly on OS X

UI

Fixed an issue on the Scenario Lobby where the mutators button was not accessible if the map could not be finished

Miscellaneous

Fixed a number of minor issues in the codebase

These are likely the last updates of the week brought by Legacy MaGog:

---------------------------

Games included in this batch:

· Airships: Conquer the Skies [In Dev]
· Lock's Quest
· Myst Masterpiece Edition
· Riven: The Sequel to Myst
· War for the Overworld

---------------------------

[Part 1 of 2]

---------------------------

Airships: Conquer the Skies [In Dev] has changed


[FILE UPDATES]

* File changed: Linux installer, English --- Size has not changed (147.0 MB) --- Version *FROM* 9.8.1.5 *TO* 9.8.2

* File changed: Mac OS X installer, English --- Size has not changed (171.0 MB) --- Version *FROM* 9.8.1.5 *TO* 9.8.2.2

* File changed: Windows installer, English --- Size has not changed (162.0 MB) --- Version *FROM* 9.8.1.5 *TO* 9.8.2.2


[CHANGELOG UPDATED] (Full changelog)

---------------------------

Lock's Quest has changed


[FILE UPDATES]

* File added: Patch (20170529 to 20170716) [Windows] --- Size: 67.0 MB --- Version: 20170716

* File changed: Linux installer, English --- Size *FROM* 270.0 MB *TO* 269.0 MB --- Version *FROM* 1.0 *TO* gog-linux-11

* File changed: Mac OS X installer, English --- Size has not changed (268.0 MB) --- Version *FROM* 1.0 *TO* 20170716

* File changed: Windows installer, English --- Size *FROM* 241.0 MB *TO* 299.0 MB --- Version *FROM* 1.0 *TO* 20170716


[CHANGELOG ADDED] (Full changelog)

---------------------------

Myst Masterpiece Edition has changed


[FILE UPDATES]

* File changed: Windows installer, English --- Name *FROM* setup_myst_masterpiece_edition_1.0_(21295).exe *TO* setup_myst_masterpiece_edition_1.0_update_(21781).exe --- Size *FROM* 513.8 MB *TO* 532.7 MB --- Date *FROM* Wed 06 Jun 2018 08:03:16 GMT *TO* Tue 26 Jun 2018 13:47:43 GMT --- Version *FROM* 1.0 *TO* 1.0 update


[NO CHANGELOG]

---------------------------

Riven: The Sequel to Myst has changed

>>> Supported languages changed *FROM* Audio and text: English *TO* Audio and text: German, English, Spanish, French, Italian, Japanese, Polish, Russian


[FILE UPDATES]

* Files removed: Windows installer, English (parts 1-2)

* File added: Windows installer, English (part 1 of 3) --- Name: setup_riven_-_the_sequel_to_myst_1.2_svm_update_(21827).exe --- Size: 805.3 KB --- Date: Thu 28 Jun 2018 11:26:23 GMT --- Version: 1.2 SVM update

* File added: Windows installer, English (part 2 of 3) --- Name: setup_riven_-_the_sequel_to_myst_1.2_svm_update_(21827)-1.bin --- Size: 4.0 GB --- Date: Thu 28 Jun 2018 11:25:46 GMT --- Version: 1.2 SVM update

* File added: Windows installer, English (part 3 of 3) --- Name: setup_riven_-_the_sequel_to_myst_1.2_svm_update_(21827)-2.bin --- Size: 1.1 GB --- Date: Thu 28 Jun 2018 11:26:03 GMT --- Version: 1.2 SVM update


[NO CHANGELOG]

---------------------------

[Part 2 of 2]

---------------------------

War for the Overworld has changed


[FILE UPDATES]

* File removed: Patch (1.6.66f3 to v1.6.66f5) [Windows]

* Files removed: Patch (1.6.66f6 to 2.0f1) (Parts 1-2) [Windows]

* File added: Patch (1.6.66f6 to 2.0f1) [Windows] --- Size: 1.0 MB --- Version: 2.0f1

* File added: Patch (2.0.1 to 2.0.2) [Windows] --- Size: 56.0 MB --- Version: 2.0.2

* File changed: DLC: Arcane Theme: Mac OS X installer, English --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Arcane Theme: Windows installer, English --- Size *FROM* 5.0 MB *TO* 6.0 MB --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Crucible: Mac OS X installer, English --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Crucible: Windows installer, English --- Size *FROM* 5.0 MB *TO* 6.0 MB --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Cynical Imp (Charity): Mac OS X installer, English --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Cynical Imp (Charity): Windows installer, English --- Size *FROM* 5.0 MB *TO* 6.0 MB --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Founders Theme (Charity): Mac OS X installer, English --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Founders Theme (Charity): Windows installer, English --- Size *FROM* 6.0 MB *TO* 5.0 MB --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Founders Theme (Kickstarter): Mac OS X installer, English --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Founders Theme (Kickstarter): Windows installer, English --- Size *FROM* 5.0 MB *TO* 6.0 MB --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Heart of Gold: Mac OS X installer, English --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Heart of Gold: Windows installer, English --- Size *FROM* 6.0 MB *TO* 5.0 MB --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Kickstarter Theme (Charity): Mac OS X installer, English --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Kickstarter Theme (Charity): Windows installer, English --- Size *FROM* 5.0 MB *TO* 6.0 MB --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Kickstarter Theme (Kickstarter): Mac OS X installer, English --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Kickstarter Theme (Kickstarter): Windows installer, English --- Size *FROM* 5.0 MB *TO* 6.0 MB --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: My Pet Dungeon: Mac OS X installer, English --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: My Pet Dungeon: Windows installer, English --- Size *FROM* 6.0 MB *TO* 5.0 MB --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Seasonal Worker Skins: Mac OS X installer, English --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Seasonal Worker Skins: Windows installer, English --- Size *FROM* 6.0 MB *TO* 5.0 MB --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: The Under Games: Mac OS X installer, English --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: The Under Games: Windows installer, English --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Underlord Edition Upgrade: Mac OS X installer, English --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: DLC: Underlord Edition Upgrade: Windows installer, English --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: Mac OS X installer, English --- Size *FROM* 3.1 GB *TO* 3.1 GB (+2.0 MB) --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: Patch (2.0f9 to 2.0.1) [Windows] --- NOTE: the download link has changed for this file

* File changed: Patch (v1.6.66f5 to 1.6.66f6) [Windows] --- NOTE: the download link has changed for this file.

* File changed: Windows installer, English (part 1 of 2) --- Version *FROM* 2.0.1 *TO* 2.0.2

* File changed: Windows installer, English (part 2 of 2) --- Size *FROM* 3.4 GB *TO* 3.4 GB (+6.0 MB) --- Version *FROM* 2.0.1 *TO* 2.0.2


[CHANGELOG UPDATED]

You can find it in post#20143 (thanks, Edward_Carnby!).

2GB -> 5GB

New languages, most certainly. I guess you're not to thrilled to re-play Riven in Japanese or Polish, eh? :P

Ultimate General: Civil War Dead Cells The following offline installers have also been updated:
-> Unforeseen Incidents to version 1.0.8 (Mac & Linux)
-> BATTLETECH to version 1.1.1-309R (Windows only)

Updated also installers for Mac.

Seriously, make separate installers for different languages instead of increasing the size and taking up more space.

New languages *and* new packaging method with less compression ;)

Talking about compression, a new weekly recap of updates is already available in the other thread. :)

Many GOG game updates have no official update flag.
I started to record it since Nov 2017. Only games I have are listed here. [1]

Report for Jun 2018:
Total updates: 104
Games updates: 88 (Some games have multiple updates, daily basis)
Flags I got: 119 (Including 3~4 weeks delayed flags for last month, see [0])

92% real updates have an official flag. 8% are missing.
All flags I got appeared after Jun 22.
I got zero flag during Jun 1~22.

Due to a system glitch, GOG hold all update flags, and started to push all of them since around Jun 22.

After the 3~4 weeks delayed flags flooding, some real updates still have zero flag:
20180615 real_myst
20180614 stardew_valley
20180613 pool_of_radiance
20180611 mafia_iii
20180607 crookz_the_big_heist
20180607 gwent_the_witcher_card_game
20180606 gwent_the_witcher_card_game
20180606 downfall_redux_copy3
20180530 star_wars_xwing_1993

False update flags:
20180627 escape_from_monkey_island
20180627 overload_playable_teaser
20180626 myst_masterpiece_edition

[0] flags flooding: https://pastebin.com/E28aY7Tb
[1] Jun 2018 real updates: https://pastebin.com/xZT9U2wr
[2] May 2018 record: https://www.gog.com/forum/general/the_what_did_just_update_thread/post19877