This is to coincide with the various issues seen recently. I have created a wishlist entry for this:
https://www.gog.com/wishlist/site/provide_a_full_and_properly_changelogged_downloads_section
Edit: added another wish list so vote on both:
https://www.gog.com/wishlist/site/more_detail_on_offline_installer_pages

The full text from the wishlist is:
In recent months it is has been noted again and again that the downloads section of the website is not fit for purpose. Changelogs do not show all changes, or in fact be present in some cases. Latest version available is broken compared to previous versions. Latest version has unwanted components. unorganised patches, main files.

What I would propse is a total rework of how this is presented. Have a folder structure for each game. Within that folder, there is a folder for each main release. Then within teach of those folders, the individual patches for that main version are placed. The user can then access this tree structure, and download the version/patches they want. This should all be accompanied with a full and complete changelog.

An example of where this is important, the first release of Wizardry 8 works fine on Windows 10, and has some additional bits. However the latest release does not work on Win10, is lacking the additional bits, and causes audio issues. Users cannot legally get the original download anymore, so they and anyone who updates has an inferior copy.
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We cannot continue to have this setup where by new installers are worse than olde ones, not documented, old versions are not available, updates not flagged, changes not described etc. It is a total shambles, has been for a long time, who could forget the helpful blue dot which until recently sometimes alerted us to a new version?

Anyways, to add substance, I link some example posts on this:
Wizardry 8 - new installer broken, no legal means of obtaining the working installer:
https://www.gog.com/forum/general/wizardry_8_not_launching_on_windows_10

Blue dots now no longer working at all - has been fixed (well, sort of) now. Leaving link here for reference.
https://www.gog.com/forum/general/has_gog_stopped_flagging_game_updates_with_the_blue_dot

Please feel free to add any other posts on said topic, support ticket is: #618084. And do vote on the wishlist.

Update 03Jan2022:
So nothing has happened, no further news. It has however been highlighted a lot recently, and will become more of an issue, that installers are getting large. There is currently no option for highly compressed archives with options to download only necessary parts of the products - e.g. language packs, compressed/hi res textures/videos. This becomes an issue as games are starting to become huge, and disc savings of tens of gb’s soon adds up. Also, if it is compressed well, I maybe in a lot of instances, not necessary to redownload every bit, just those sections that have been updated thus saving quite a bit of bandwidth.

Yes.

While in general I agree with e.g. good changelogs and such, I am not sure I want that kind of overhaul with a specific "folder structure" etc. Reason being I'm afraid it would break e.g. gogrepo, or make it too complicated to handle. I prefer a clean and simple system.

EDIT: I elaborate a bit what I mean here. For instance, if there are several different versions to download and I want to download only the newest one... depending how GOG had implemented it (e.g. by just listing all the different version numbers), it might be very hard if not impossible for a script like gogrepo to try to understand which of them is the newest version. Like with Wizardry 8, how can the script decide which of these versions is newer:

setup_wizardry8_2.0.0.6.exe
setup_wizardry_8_2001_12_23_(22306).exe

So for now I will not vote for the wishlist, but I am not totally against it either (at least for getting better changelogs). As noted by me and someone else in that discussion, for us the newest Wiz8 offline installer works fine in Windows 10. No sound or other issues.

Yeah it would be nice to have a changelog to see what changes have been made, in case they cause the newest version to fail on some Windows 10 systems (and possibly make it running better on some other systems, who knows?).

Adding MD5 or SHA checksums for each file would be useful, too.

Yes, but hopefully they will use SHA256 and not MD5 or SHA1 (as the latter two are insecure).

I think all the installer files do have md5 checksums, but they are not visible in the web page. There is some way to get them as that is what e.g. gogrepo apparently does.

Extras which are in zip files can be of course checked by testing or uncompressing the zip files. I think MD5 is quite enough for checking that a downloaded file is not corrupted.

SHA256 etc. are needed if you need to make sure no one has intentionally tampered with the file, but I personally don't consider that important as I don't expect GOG staff to tamper with the files.

Good idea.

I would be more concerned about them not keeping old versions available, than about GOGrepo working. If GOGrepo downloads the newest version, but the newest version itself doesn't work outside of the "optional" Galaxy client, then did GOGrepo really download anything worthwhile?

Whilst I agree with your points, and don’t want to break gogrepo for those who use it, this in an implementation decision, not really part of the idea. I would probably keep the current part, so latest is still shown as is, and then have another option, like the other-changelogs, which then allows access to all the older versions and patches. That way nothing changes for most users, but in addition it’s possible for those who want/need to, to be able access other versions.

The change logs need fixing irrespective of anything new/to be changed as they are quite up informative at the moment.

GOG do provide MD5SUM for about 99% of their installers.
For integrity checking, MD5SUM and filesize combined are enough.

However, GOG do not provide MD5SUM for their game goodies.
You can check zip files with associated tools, but not all GOG game goodies come in a zip file format.

Sure, I'm also content with them for the moment, as there are yet to be any (second-)preimage attacks on it, so for the specific purpose of verifying a file created by a trusted entity, it is sufficient. However downloads via HTTP are vulnerable to man-in-the-middle attacks, so they are also necessary if one does not make sure to force HTTPS.

No reason we can’t have both though. Games should have a release date, to coincide with changelog, so it’s only a matter of the latest being at top. I do agree though, if the latest version is broken, or less value than a previous one, then is it worth keeping at all.

Oh, I suppose we should bear in mind that anything gog do update will likely break 5 other and/or upset part of the userbase, so have to factor that in as well.

As for the optional client, afraid that is not going to change

I'd just like them to label patches under one thing. Rather than going by one naming system for one game, another for something else a third for another.

Just slap the first release on GOG as 1.0 then call every patch 1.01, 1.02 etc.

Yes, that's exactly what I had in mind - checking for download errors not as a security measure, so any checksum type will be fine.

In 99% of the cases, the latest installer is what I want. And that is kinda the industry standard method of doing things, I don't see e.g. Humble Store or IndieGala offering several versions of installers, they only provide the newest one they have. If the newest version has some critical problem, then it is naturally up to the developer/publisher to fix it.

Also, gogrepo doesn't delete any older installers automatically, it is up to you to decide whether you want to delete older files or not. I have e.,g. kept the earlier CD and DVD versions of Myst 2 Riven (on top of the newest version which is the ScummVM version), and I also decided to keep the original "Among the Sleep" out of curiosity, just to see how it differs from the Enhanced Edition. Yeah I guess that could work. So as said, it depends how they'd end up implementing it.