I really liked Crysis 2. The music and other sound stuff was great (and let's be honest, you should always rate games solely by their music).

I liked vanilla Crysis more than Crysis Warhead, so if you haven't played it, consider giving it a go.
In Crysis you play as this guy Nomad. You go around in the jungle and sneak up on guys a lot, and if they find you and go all "U mad?", you can go all "Nomad".
In Crysis Warhead, you play as the Guvnor and go around turning people into muppets, and do much of the stuff of vanilla too, I guess.

/edit: I decided to elaborate about Crysis 1&Warhead

Wow that's pretty hardcore. Anyway GOG has said they're looking into adding new games to the list as soon as they can.

Anyway I recommend (some of the games have already been mentioned by others):

Saints Row The Third
STALKER CS and Call of Pripyat
Arkham Asylum and City
Deus Ex HR (I gotta replay this again <3)
Minecraft (well you said FPS, and Minecraft is FPP and you can use guns for some mods, and it is pretty taxing on the PC...)
Borderlands
Fallout New Vegas!

So Warhead is less stealthy than the original?

I just assumed it was going to be basically the sandboxy missions that I liked about Crysis without the silly "Crysis of Duty" end half.

CRPG:
Drakensang, and its sequel River of Time
Divinity 2
Dragon Age: Origins (but not Dragon Age 2. 2 is not horrible, but not worth your time either)
Vampire the masquerade: Bloodlines (with fan patch!)
Fallout New Vegas
Alpha Protocol
Skyrim
The Witcher

Strategy:
Civilization 4 (and possibly 5, I have not played that)
Victoria 2
Crusader Kings 2
King's Bounty: The legend
Sword of the Stars
Galactic Civilization 2
Europa Universalis 3 & Rome

Adventure:
Frogware's Sherlock Holmes Series (though not the first one, Mystery of the Mummy)
Dreamfall
The Void
Penumbra
Amnesia
Scratches (get Director's Cut)

Action:
Deus ex Human Revolution

At first I was like "ehh, I'll get it later." Then I saw how much it was marked off for. So I just bought it. Should be lots of fun, and looks like it will provide an appropriate level of eye candy.

I don't actually remember much more than that I liked Crysis more than Warhead, and that you play as Psycho (I made a silly Brit jest earlier, sorry about that) who has a muppet fixation. I remember some sneaking, and a lot of running around with big guns (given the chance, I often take the machine gun and make things explode). It's much more like vanilla Crysis than Crysis 2 is anyway.

My opinion might be biased since I played vanilla first, and Warhead was kind of "more of the same" (not a bad thing, just doesn't have as much impact).

In Crysis 2, you can pretty much sneak through most of the places without killing anyone, but the cutscenes still say you killed everyone.

After my "no detection and perfect pacifist" playthrough I've been meaning to go through playing the biggest, bloodthirsty Jensen I can:) I just hope there's enough bullets.

Trust me bro, it's awesome and really lives up to the legacy - and I'm saying this as a purist who disliked Invisible War. I mean, shit, you can even have the choice of playing the game without going third-person at all. That's how much they respect the franchise.

Deus Ex HR, Mass Effect 2, Skyrim, Just Cause 2 and Fallout New Vegas are my favorite games of the last few years.

Sounds like I'll be checking that box the moment I start the game up.

Alan Wake
Assassin's Creed 1, 2, Brotherhood & Revelations
Batman: Arkham Asylum & Arkham City
BioShock 1, 2 & Infinite
Braid
Bully: Scholarship Edition
Costume Quest
Dead Space 1 & 2
DeathSpank, Thongs Of Virtue & The Baconing
The Elder Scrolls IV: Oblivion & V: Skyrim
Fallout 3 & New Vegas
Grand Theft Auto IV & Episodes From Liberty City
Half-Life 2, Episodes One & Two
Just Cause 1 & 2
L.A. Noire
Left 4 Dead 1 & 2
Limbo
Mass Effect 1-3
Max Payne 3
Mirror's Edge
Portal 1 & 2
Rayman Origins
Resident Evil 5
Sonic Generations
Stacking
Super Meat Boy
Super Street Fighter IV: Arcade Edition
Vessel
World Of Goo

And here I thought this topic was for requesting newer games to be added to GOG. LOL, that'll teach me to assume. But since I'm already here.......I'd love to see Supreme Commander pop up on GOG sometime in the near future. Feel free to bump this post to a more appropriate thread if one exists for requests. I couldn't find one.....