Arkham Asylum is a really great game, even if you aren't a batman fan but like most things like this, it doesn't hurt to be one either. It appealed to me because it didn't just go straight up Dark Knight the movie batman, which I throughly enjoyed (I think I saw it at least four times in theaters and three times on Blu-Ray.) it felt more in line with the early 90's animated series but with a more darker twist. Plus getting Kevin Conroy as the batman and Mark Hamill as the joker back from the animated series was such a great touch and it brought my childhood rushing back like a tusnami.
Also, by the time you get around to Assassin's Creed 2, both of the DLC should be out then, which I think one is three dollars and the other is five, something like that. I don't know if you have your PS3 online, but the option to expand the game is there especially since what happens in the DLC is relavant to the games storyline not a "okay, so you beat the game. Here's some random shit with little consequence you can do. Bye." :p
Out of curiousity, what of Uncharted 2 made you feel it wasn't as good as the first? If Bioshock didn't come out that year, the original Uncharted would of been my prime pick for my game of the year I had so much damned fun with it. Did the storyline in the sequel kinda of just fizzle out or is it the sort of things where it feels like it just drags on a little bit and would of been better suited to end eariler? Uncharted 2 is one of the driving forces of making me keep my PS3 around, so I'm pretty excited to get around to it someday.