It's amazingly good and goodness it can be impossibly difficult at times. At the start I had 5/5 health/eve so couldn't pick up anymore for a while and everything was dying, so I was all "pfft, this is gunna be easy"... I was so wrong, so many times I'm cursing myself for running out of ammo at the wrong time, and the music is so atmospheric. It's so much more than the original was and after playing it all day I'm still (hopefully) not very far through!
In context, I got Halo 3 for the 360 yesterday (well, day before yesterday now) and blitzed through it in a day, Bioshock 2, amazing.
I'm getting constantly great framerates too, 1680*1050 with settings on High and it'll settle between 40-60fps (I have v-synch on) and that's with not exactly a powerful system.
Intel Pentium Dual Core E6500
6GB DDR2 RAM
320MB EVGA 8800GTS
Windows 7 X64
I'd still be playing now if sleep wasn't calling me saying "oi, come here and get some sleep"
Downsides are the DRM infestation, it also reinstalled Windows Live thingy, which hooks in with my XBox live gamer tag thing, sorta breaks the immersion when you're at a tense spot and get a message pop up from a friend.
So far I'd have to say it's probably among the best FPS's I've played, the story is great, the visuals are pretty darn good, enemies AI is jaw droppingly funny at times and having a little sister on your shoulder when you set fire to a monster and she says "ohh, marshmallows" or something is just surreal.