Dark Souls, I've tried it for the very first time recently and I totally loved how this game respects gamer and doesn't treat him as an idiot like f.e. Mass Effect does

Yeah it's pretty great

I really like DMC (the devil may cry reboot). Finished it last night and actually restarted today on higher difficulty. A rare treat these days because mostly with newer games i uninstall immediately after finishing. Games have become to much a disposable commodity these days. Finish it once and never look back. Glad this one was different.

Only if you want to get it legally...

Bravely Default. Best final fantasy ever.

I was so Lucky i picked it up when I did. I had no idea it was going to disappear and I bought it and a couple of days later it was gone...

Tales of Maj'Eyal. It's not just good, it's also darn addictive. At first I just thought it felt like another roguelike, but once I got into it, I realized just how deep it is, and how much content it has.

If anyone wants to try it, you can get it for free, or if you want to support them, you can buy the game on steam or Gamer's Gate, and that will also give you another class and some other minor things.

Lego Marvel Superheroes.

First game I've ever completed the story and then hung around to pick up collectibles. I'm still at ~27% complete!

Flying and vehicle controls suck big time, though. Like, literally the worst I've ever used. And no invert y-axis option. Really frustrating on the races.

I'm not really selling this, am I? :P

Heartstone. I find it really fun making up different decks and test them out. Been playing it casually a couple of months now and doing alright. I find it fun trying out gimmicky deck and see just how far i can get with them. My paladin based around the theme of divine shields and healing has been doing surprisingly well considering i lack any of the really good cards for it. (Tirion, Blood Knight, Sunwalker, Equality)

Jagged Alliance 2 (with the awesome 1.13 mod)
I can't believe I waited this long to try it for the first time :P

Well, it may look like a platformer, but it's usually classified as "3D action-adventure". You jump automatically in that game. While at times you need to rely on your reflexes, the focus is on exploring the game-world and puzzle solving. While the story is quite bland, I think the main reason why the game is considered that great is because of its playability (at that time it had some pretty new mechanics in it, e.g. target-lock, context-sensitive action button, mini-maps) and game design (especially the dungeons). It just all fits together. Exploration, puzzles, combat, hidden items and so on. Definitely worth a try. And nothing I have ever seen in a PC game in this perfection.

Regarding games on GOG which come close to that game (in its gameplay, not in its perfection) and arguably copied some of Zelda's concepts are Psychonauts and Beyond Good and Evil. You can jump in those games, though, so they are more "platformy" than Zelda.

SMT Devil Survivor 2 great, but the first one was better.
Betrayal at Krondor
Conquest of Elysium 3, both good games too.

Oddworld: Stanger's Wrath. one of the most unique FPS games out there. Weapons are fun stealth is encouraged in a meaningful and fun way. the game looks great, the story ends up having surprising impact and I loved the fact you are always kept in the game world rather than being teleported around. The game has the perfect amount of challenge for me and best of all I enjoyed the boss battles..... that cracking sound you can hear is hell freezing over!
You also get to use boat!

I recently finished Fable the Lost Chapters. another X-box classic on PC. Despite some glaring flaws (I got the bad ending by mistake >:c) I really had a good time with it. I hope GOG gets more X-box games.

dark souls ii, but I knew it was gonna be good :-)

S.T.A.L.K.E.R. - Lost Alpha

A serious Game of the Year contender! And it's free!