I'm enjoying this game so far. It reminds me A LOT of Mass Effect, to the point where I keep pressing Y to heal myself. The dialog trees are especially... reminiscent? I don't want to say "blatant ripoff," but, yeah, you pretty much get three answer choices for questions, one good, one neutral, one evil. Then you sometimes get answer choices that have to do with your skills, which is similar to the charisma/intimidation in Mass Effect. Then, of course, there's the whole RPG-shooter hybrid thing going on.
Aside from all that, the atmosphere in this game is much creepier. I haven't been able to recruit anyone yet (I'm not even sure how that works), so I'm by myself all the time. The first time I stepped on a frag mine and it blew me up, I think I jumped a few inches off my chair. I was underground in the train tunnels, then all of a sudden there's some beeping, then a BOOM, then there's blood on the screen. I was not expecting that.
Right now, I'm taking a break from Fallout 3 to play Mercenaries 2, which I just got from Gamefly. It's a lot more fast paced, which is nice, and I haven't experienced nearly as many bugs or glitches (ie - Fallout has frozen on me once, and I've seen about a dozen graphical glitches). And it's not as serious, which is also nice. Fallout is kind of heavy to spend a few hours with it every day. For me, at least.