Toss up between Dragon Age Origions and Divinity 2 both are good in different areas

I can't decide between Fallout 1 and Gothic 1...

Beyond Good and Evil for me, I didn't even know it excisted until GOG got it. Completed it within a couple days which for me is quite fast.

WoW. Probably because I'm having so much fun with the guild lately. :)

Operation Flashpoint: Elite

Mass Effect. It was a real bargain for $10 and I have spent more hours on it than all other games combined this week.

NWN2: Storm of Zehir.
Great cRPG. Possibly the best thing Obsidian have done.
Honourable mentions for Battle for Wesnoth, which is a fantastic indie strategy game, and Ben There, Dan That a fantastic indie adventure game.

It's between Batman and Mirror's Edge for me. Both were amazing in their own ways. Batman had some moments that really blew me away, like....
*****SPOILERS*****
When you walk down a hallway that turns into the alley where Bruce's parents died.
*****END SPOILERS*****
But Mirror's Edge is the kind of game I'd rather play. Dice has been awesome lately.

<span class="bold">Fat Princess</span>
This is the best CTF game I've played since SubSpace's War Zone variant kicked the bucket ten years ago.
Best game I played for the first time: World of Goo
Best game I played at all: Shadow of the Colossus

I'm going to have to agree with everyone else Batman was completely excellent and I'm working through Dragon Age right now which is also a stellar game. Surprise hit for me this year though was Burnout Paradise on PC. I played that far more than I expected to.

Dragon Age Origins / Machinarium.

Tough one. Hmm. Dawn of War 2.

I haven't played Dragon Age because I like to wait until sub-$20 pricing.
Games that were new (to me) this year that I spent a lot of time playing include Baldur's Gate, Oblivion, and (recently) Mass Effect. They're all good for different reasons - it's hard to choose the best one.
Older stuff that I played a lot: Dawn of War, Warcraft 3, Diablo II, and way too much Team Fortress 2.
[edit]: I bought both Planescape: Torment and Icewind Dale toward the end of the year and have barely started them, figuring I would rather finish Baldur's Gate (and BG2) first, so depending on how long that takes, I expect that PS:T and IWD will rank highly either in 2010 or 2011. Yeah, I like good OLD games!

Hmmm Idk... I finished a LOT of games this year.
Fallout 3, Planescape Torment, and Gabriek Knight are my favorites of the ones I finished this year, with Castlevania: Symphony of the Night close behind.

New Prince of Persia or Stalker: Shadow of Chernobyl
The first made me feel cooler than any other game, the way I was flipping around and scaling impossible looking stuff. It also looks absolutely beautiful, moreso than any other game i've seen since Shadow of the Colossus. I am in awe of this game and its production values.
Stalker drew me in like no other game. It also made me feel really cool in that I have never needed to rely on my own wits so much. I even have a bunch of pieces of paper spread across my desk with directions to in-game stashes and other important info hastily scrawled on them. In fact, I think I'll go resurrect that Stalker stories thread from a while back.
Assassin's Creed was pretty awesome too. I just like climbing on things.