Bethesda happened...

Some of GOG's best FPS games are Outlaws and FEAR. The former is an animated western game with great music, and the latter is a survival game with a ghost motif!

The Saints Row series is very good as well. They're like a wackier GTA series. I would recommend the 3rd version. Praise Genki!

If you want to try some indie retro-styled games, I would suggest Shovel Knight and Freedom Planet!

How about rare, fun games that really needed sequels? Try Hostile Waters and Rogue Trooper!

Want a fun racing game with demolition derbies? FlatOut 2!

Wasteland 2

Heavy on the RPG with excellent TBS combat.

There's also all of the Jagged Alliance games. Other top games IMO are: Interstate '76, The Longest Journey, Planescape: Torment, Arcanum, System Shock 2, FarCry, Gabriel Knight Series, Gothic, Hitman, Thief, Inquisitor, Pathologic, Project Eden, Tales of Maj'Eyal.

If you haven't already, you MUST take a look at Outcast. It's a fantastic hybrid of platforming, RPG, adventure, stealth, and shooting. It deserves to be ranked among other classic RPG hybirds, IMO.

System Shock 2 is also a must-play, if you like STALKER and Deus Ex.

Don't think Nox has been mentioned yet. Try it.. It's fun..

Some games i do like much: Master of Orion 2, Spacerangers HD, Lands of Lore, Battleworld Kronos, Battle Isle + History Line, Ultima Series, Dungeon Master ... all are strategy or RPG and all are very good :)

Just be warned that while Metro absolutely kills it in terms of atmosphere, its gameplay is lacking when compared with STALKER. It's very linear, and follows the linear FPS formula a bit too closely, even when it harms the atmosphere (i.e, explosive rail shooting segment that comes out of nowhere and kills the sense of lonely menace).

None of this is to say it's a bad game, but just don't expect STALKER.

Oh, another suggestion! If you can deal with a brutal BRUTAL difficulty/learning curve, The Void is INCREDIBLE. I can't even really describe what sort of game it is, it's just really unique and beautiful.

Well, answering your title question, and deviating from your OP request, I'll keep this down to a personal opinion post and heartily recommend:

- Nox
- Sanitarium
- Psychonauts
- Grim Fandango (Remastered)
- Indiana Jones and the Fate of Atlantis
- Sam & Max Hit The Road
- Outlaws
- Wing Commander III: Heart of the Tiger
- Realms of the Haunting
- Loom
- Stick it to the Man
- The Cat Lady
- Primordia
- Pathologic
- The Legacy of Kain Eidos series (Legacy of Kain: Soul Reaver; Soul Reaver 2, Blood Omen 2 and Legacy of Kain: Defiance)
- Beyond Good & Evil
- Bad Mojo Redux
- Super Time Force Ultra
- Not A Hero
- Ether One
- Hotline Miami (and, to an extent, Hotline Miami 2: Wrong Number)

So, yeah... hahaha! Quite a big list, with varied (but mostly adventure-based) genres, which I don't think are much to your liking, but are some of the games that came to mind when I thought about *my* favourite games on GOG. Some are old, some are new, ranging from... "cult classics" to modern indies.

You should take a look at the "GOGmixes" :
e.g. http://www.gog.com/mix/totalbiscuits_definitive_list_of_strategy_games

I don't really play strategy games, as for RPGs, you probably played Planescape: Torment already? Other than that, I quite enjoyed Arx Fatalis, Gothic, Shadowrun Dragonfall, Divinity 2: Director's Cut, Nox, lots of great community module for Neverwinter Nights, Driftmoon (RPG-lite adventure/exploration game), Lands of Lore: The Throne of Chaos (if you're also into dungeon crawlers) and Enclave (more action than RPG but lots of fun regardless). Vampire the Masquerade: Redemption's gameplay can be a bit tedious compared to the missing Bloodlines, but it's still worth playing for the setting and atmosphere.

This. It was well-received back in the day and has garnered additional late recognition but in my opinion it's STILL underrated. It's easily one of the most immersive and engaging RPGs I've played, ironically largely thanks to it not trying to too hard to be an RPG but rather an action adventure.

As for strategy: Total Annihilation is fantastic, albeit a bit slow at times. I can also wholeheartedly recommend KKND (rather the first one, not that big a fan of the sequel) to anyone who likes the C&C style RTS games. Then there's of course Earth 2150, a really unique and great early 3D RTS game. Ground Control 2 is also a great choice if you're interested in fast-paced tactical games. It's much better than Ground Control 1 and the story is so unrelated that it's perfectly unnecessary to play GC1 first (I regret to this day that I only tried GC2 after forcing myself through the boring and frustrating GC1 campaign).

The word you are seeking is 'sold'.

Half-life 2 - Episode 3 - Electric Boogaloo

...or Deus Ex. Depends on my mood...