Which game should I beat next?

I just beat Deus Ex: Human Revolution not too long ago (and I really enjoyed it!) and it made me realize that although I've played a lot of games, I haven't really beaten that many in the past few years. Since Steam sales have been so generous, I actually have quite the backlog, and I want to work my way through some of it before I buy (the many good) new games coming out. But it's difficult for me to settle on just one game, so I figured I'd let you all decide. Whatever has the most votes after 3 days (I'm sure it will be ignored in the first few hours), I'll commit to beating. Any comments, tips, hints, thoughts, feelings, etc., about the games are also welcome.

Thanks everyone for your input!

Batman is nice and quick, about 8-10 hours. Its a great game and you can quickly move on to something else.

I'd go with Witcher, ME 2, Batman:AA, if you manage to finish them in the next month you'll be just in time for Batman Arkham City :P. Never really got into Chronicles of Riddick, same with VTM:B, never was crazy about vampires.

Witcher 1 would be a good first choice because it's heavy on the story and dialogues, gets you involved, the beginning is pretty awkward but it'll get substantially better after the introduction. ME 2 would be a good, cinematic, light game that lasts for quite a while and finally Batman is one of the best superhero, stealth games released in the last years, with the sequel getting released early next month.

I loved Vampire the Masquerade. Now that you reminded me of it, I kind of want to go back and play it again.

Vampire The Masquerade. Start with the classics and work your way up. =) Many times the classics end up better than the new iterations.

I voted Batman but in reality, I think you should play a game that is the most different from Deus Ex as possible, justm to provide variety. In other words, Batman or The Witcher would be a good idea.

Mass Effect 2 then Vamp the Masq