The Ultima series

Wasn't aware, thanks :) And a few other interesting adventure games as well I see

The entire Wing Commander series

I'm not sure if I'm interpreting this correctly. For the longest time the GOG's community was indeed the best part about GOG. But considering the recent changes, and the droves of old members swearing off the forum due to the multitude of attacks from new/other old members, and the fact tinyE is posting this, makes me think this is a sarcastic post. So I took it as that, and chuckled, just like tinyE intended. :)
The HD edition on STEAM is a bad joke. There are no HD assets added, it's all a lie, because they faked the old assets to make them look bad. And the STEAM version is missing the 2 expansions, which add a tremendous ammount of content to the game.

The HD edition, is severely incomplete.

Wow so the complete edition on gog is unique indeed nice

for better or for worse, it was not a sarcastic post.

What really defined GOG for me was bringing the Baldur's Gate games back so that they legally could be bought again. And for a short while they were actually GOG exclusives. However, this is not the case any more and even worse, they have gone even from here and are replaced by some kind of enhanced, more expensive editions. So it's a thing of the past.

In principle I would count all the popular classics that GOG brought back first, even if they are available somewhere else too now.

My first thought are Warhammer 40k games (those from 90'):

Warhammer 40k: Chaos Gate
Warhammer 40k: Rites of War
Final Liberation: Warhammer Epic 40k

First classics on GOG (well, maybe except Final Liberation :P) which I was genuinly interested but to be honest didn't believe that we will ever see themin GOG's offer. (worth to mention, that those are three amongst 12 positions in (current) GOG library which have GOG as publisher).

Probably something similar (aside from the fact that GOG is not publisher :P) is Jazz Jackrabbit series.

In fact, I think that those "symbolic" games are also such titles like System Shock series, Star Wars Galactic Battlegrounds etc - they're nowadays available on Steam, but it's GOG who "digged them out" first and made incredible job to bring them back to life. They're still something which in my opinion are GOG's "badges".

Plus some small games, like Eador: Genesis - again, it's available on Steam, but it was GOG who first "caught" it and brought outside the Russia.

Apart from the titles already mentioned above (like Albion, Ultima series, Forgotten Realms The Archive Collections, Al-Qadim, Infinity Engine originals, NWN 2), GOG also sells quite a few more old RPG classics exclusively, such as:

D&D: Dark Sun series
D&D: Ravenloft series
D&D: Krynn series
Nox
Revenant
Lands of Lore Trilogy
Ultima Underworld 1 + 2
Rage of Mages 1 + 2
Evil Islands
Anvil of Dawn
Ishar Compilation
Thunderscape
Entomorph: Plague of the Darkfall
Battlespire
Redguard

I dislike forced exclusivity like they were trying to go for with Thronebreaker, but I very much appreciate GOG giving a home to the underdogs that noone else seems interested in anymore.

Sweet recommendations , just noticed this trilogy was actually free , i am sure its not on anywhere else

jill of the jungle

https://www.gog.com/game/jill_of_the_jungle_the_complete_trilogy

They sell those on Steam.

And despite your edit, they still sell those on Steam. :P

0 games bought, account made October 2018.
Most if not all your posts and reviews are just flaming.
Get the fuck out of here.

Not replaced by -- bundled in with. For the purposes of this topic, all the D&D games that Beamdog messed with and re-released (Baldur's Gate, Baldur's Gate II, Icewind Dale, Planescape: Torment and Neverwinter Nights) are still unique when purchased here, in that the GOG versions all come with a copy of the old "complete" GOG release -- including all their bonus goodies, AFAIK; copies purchased elsewhere don't.

Project Warlock. It just came out and isn't on Steam.