Yeah, I emailed their support about the missing Hamlet dlc which they replied they currently have no plans to release it on GOG.

I then asked about at least getting Steam keys for Don't Starve and the all the dlc which I have on GOG. They said they could give me Steam keys for the base game and the multiplayer version Don't Starve Together, but not the Reign of Giants or Shipwrecked dlc I already own on GOG. Really disappointing, and i'm not paying for something twice just to get proper support.

Thank you omega64 and ElTerprise for keeping the list up to date. I'm quite stunned that Devolver Digital and THQ Nordic GmbH are the worst offending publishers.

Removed:
My Friend Pedro
Soundtrack has been added.

GOG hasn't announced it, just like with another recent soundtrack. They're really bad at this. :P

Again without announcement:
Removed:
Graveyard Keeper;
Phantom Trigger;
Hello Neighbor.

Edit:
Lovely Planet;
Clustertruck.

All of these had the soundtrack released. Only Party Hard 1 and 2 to go then with Soundtrack and DLC.

Warhammer 40k Mechanicus
Missing Linux build, although it was originally advertised

Not really surprising.

Only when a company takes GOG seriously enough to bring their games here on day 1 (or at least close to release) can they get behind on updates at all.

Companies who use GOG only as bargain bin for their back catalog games that have long since stopped receiving updates can hardly be behind on updates, can they? Now that would really be surprising and not reflect very highly on them.

:)
But I think it's unfair just to pick Omega and me, there a lot of people working on it and keeping it up to date, not just the contributors Alexim, PookaMustard, Rosalumina, Sanfueg, Solus, Zeogold, Omega and me. Without the help of the people posting here, notifying us about new issues, that wouldn't be possible at all.

It's actually not that surprising because we list all kinds of different issue types and honestly quite a few games end up here for not providing a soundtrack DLC on GOG. Imho something annoying but not as severe as games that are either missing (critical) updates or features (sometimes even features that were advertised on the store page).

The "worst offenders" are just the ones that just show up way too often on the list for several reasons which is why we call them "appear most often", really the worst offenders are the ones that treat GOG so bad, that they got a special mention (and neither Devolver nor THQNordic are among them).

Venetica Gold Edition.

GOG is missing the "Artbook, Soundtrack and never-before seen pitch documents/trailers". These are included in Steam's version and were added to make it the Gold Edition in 2015.

Added:
Panzer Corps
Star Hammer: The Vanguard Prophecy
Warhammer 40,000 Armageddon

are all missing the Mac build

60 Seconds! Reatomized - released on Steam (27/7), as a free upgrade for previous owners - not here at all - emailed devs - no response as of yet

Yeah, we noticed before release already. Let's give them a few days to be sure it's not coming though.

Updated:
Anima: Gates of Memories
* missing paid Soundtrack DLC

Added:
Headlander:
* no standalone Soundtrack DLC, Soundtrack is only available in the Headlander + Soundtrack Edition