Just finished Single Player Campaign for Spec Ops: The Line (PC).

So here's My Games Finished in 2012 List, all updated:
http://www.gog.com/en/forum/general/games_finished_in_2012_1/post796

Finished Deus Ex: Human Revolution 3 times over; just love it. Since i'm way behind in games and there are 40 billion on the backburner, I've finally finished Fallout 3 too.

Finished Shatter. An excellent variation on the brick breaker theme, after completing Wizorb not long ago !

It would be difficult for Shatter to be more different from Wizorb than it is! ^_^ Crisp graphisms, excellent soundtrack (hell, the soundtrack alone could almost be a good reason to buy it!), challenging levels, clever bonuses... Almost a flawless game.

Yes, almost, because:
* I finished the story mode on normal in a little over 3 hours which is not long at all (but it's normal mode and there are other modes than story mode)
* sometimes, there are so many things on screen that it's quite easy to loose track of your ball...

But now I'll pick up a different style of game... ;)

So far in 2012 : http://www.gog.com/en/forum/general/games_finished_in_2012_1/post15

Finished Jolly Rover: it was quite enjoyable although some puzzles were quite illogical near the end. The references to Monkey Island were a bit too much.

06/01/2012: Magic: the Gathering - Duels of the Planeswalkers 2012
09/01/2012: Portal 2
17/01/2012: Bloodrayne
18/01/2012: Gabriel Knight: Sins of the Fathers
27/01/2012: Space Rangers
28/01/2012: Gabriel Knight 2: The Beast Within
15/02/2012: Fortix 2
18/02/2012: Alpha Protocol
11/03/2012: Deus Ex: Human Revolution
17/03/2012: Deus Ex: Human Revolution - The Missing Link DLC
06/04/2012: Shank
06/04/2012: DLC Quest
07/04/2012: Lume
16/04/2012: Faerie Solitaire
21/04/2012: Assassin's Creed: Director's Cut
05/05/2012: Botanicula
06/05/2012: Machinarium
16/05/2012: The Witcher
29/05/2012: Quest for Glory 1 Original
01/06/2012: Quest for Glory 2 Original
04/06/2012: Quest for Glory 3
12/06/2012: Puzzle Kingdoms
17/06/2012: Quest for Glory 4
11/10/2012: Carmageddon: Nice and fun, with the exception of beating the suppressor. Unfortunately, my biggest beef with the game is that you can only drive Electric Blue after you've finished all the stages, but it would make the earlier stages so much easier (and more enjoyable).

Complete List http://www.gog.com/en/forum/general/games_finished_in_2012_1/post1050

Prince of Persia Warrior Within (first time in ages i have completed a game on hard)
Prince of Persia The Two Thrones

I finished HALF-LIFE 2 Episode 1 a few days ago. ^^ Very cool.

Triple header this time.

Dirge of Cerberus. I actually kind of like the idea, but the execution/gameplay was a mixed bag because of trying to mix rpg and action elements and leaning a bit too heavily towards rpg elements instead of something that played smoothly. Also it felt like the bosses were too much easier than some of the normal stage missions/enemy placements.

Genji: Dawn of the Samurai was incredibly pretty, but also extremely shallow.

Ratchet: Deadlocked. Eh. Basically a tacked on single player campaign for a multiplayer game. Yeah it's a bit repetitive (like the commentary) but still kind of enjoyable though. Still better than Size Matters.

Dark Lord
Super Robot Wars OG2
Ys 4: Mask of the Sun
Castlevania
Final Fantasy 4 Interlude
Duke Nukem 3d
Jamestown
Blocks That Matter
Final Fantasy 13 (Platinum)
Fragile Dreams
Fallout 1
Breath of Death 7
Hyperdimension Neptunia (Platinum)
Solatorobo
Tales of Graces f
Sands of Destruction
Batman Arkham City
New Super Mario Brothers Wii
Final Fantasy 3 DS
Alpha Protocol
Final Fantasy 13-2
Rune Factory 3
Pikmin
Dragon Age Origins
Halo 3
Phantasy Star 3
Klonoa: Empire of Dreams
Little Big Planet (PS3)
Ratchet & Clank Future 2: A Crack In Time (Challenge Mode/Hard Mode/Platinum)
Xenoblade
Superbrothers: Sword and Sorcery
Persona 3 Portable (mshe)
Prince of Persia: Sands of Time
Metroid Other M
World of Goo
The Last Story
Divine Divinity
Final Fantasy: 4 Heroes of Light
Dirge of Cerberus
Genji: Dawn of the Samurai
Ratchet: Deadlocked

I finished The Witcher 20 mins ago :D

Personally, I thought the sequel was a lot better than the original. I'm playing the original through again using the enhancement method linked here on GOG using both games, and it's exciting to get back into, but I'm honestly getting impatient and find myself wanting to get to the second game. I'd highly recommend giving it a shot.

Recently finished Unreal Gold and wow, was that an enjoyable experience. Exploring the levels, finding out how to progress to the next area with no need for a map marker, was extremely engaging. Initially, I had a bit of trouble figuring out what to do, and resorted to a walkthrough for assistance, but over time got better and knowing what to look for to progress. The Na Pali world was interesting, and the amount of different environments presented in the game was amazing. There's a lot of content in this game.

Overall, it was refreshing to play a FPS that was free of cinematics, map markers, and other elements that dot a current day FPS.

Also, the music was amazing! https://www.youtube.com/watch?v=--5COmk8ZM0

So far:
Just Cause
Cave Story+
Area 51
Need for Speed: Hot Pursuit
XIII
Star Wars: Jedi Academy
STALKER: Shadow of Chernobyl
Metro 2033
Deus Ex: Human Revolution
Mirror's Edge
Thief II: The Metal Age
Alan Wake
Deus Ex: Human Revolution - The Missing Link
Alan Wake's American Nightmare
Unreal Gold (including Return to Na Pali)

Blocks That Matter
including the Chocolate Update and the bonus levels, except for An Ice Glitch and Extreme Temperature.

Professor Layton and the Spectre's Call
except for the final puzzle and the second to last weekly puzzle.

Rayman 3
got all cages, have access to all arcade games, of which I didn't finish Racket Jump, Razoff Circus and Balloons.

Sanitarium

I see the list hasn't been updated recently.

06/01/2012: Magic: the Gathering - Duels of the Planeswalkers 2012
09/01/2012: Portal 2
17/01/2012: Bloodrayne
18/01/2012: Gabriel Knight: Sins of the Fathers
27/01/2012: Space Rangers
28/01/2012: Gabriel Knight 2: The Beast Within
15/02/2012: Fortix 2
18/02/2012: Alpha Protocol
11/03/2012: Deus Ex: Human Revolution
17/03/2012: Deus Ex: Human Revolution - The Missing Link DLC
06/04/2012: Shank
06/04/2012: DLC Quest
07/04/2012: Lume
16/04/2012: Faerie Solitaire
21/04/2012: Assassin's Creed: Director's Cut
05/05/2012: Botanicula
06/05/2012: Machinarium
16/05/2012: The Witcher
29/05/2012: Quest for Glory 1 Original
01/06/2012: Quest for Glory 2 Original
04/06/2012: Quest for Glory 3
12/06/2012: Puzzle Kingdoms
17/06/2012: Quest for Glory 4
11/10/2012: Carmageddon
16/10/2012: XCOM: Enemy Unknown: Not sure what was the last game that I just sat and played (almost) nonstop, but I did enjoy this one immensly. Highly recommended, but make sure you don't expect the original. Also, be prepared to start over again (and again, and again), it is unforgiving.

Add Legend of Grimrock to the list :D