I really, really liked the approach to the elevator, when the lights are turning on for you. The feeling of old, left-behind technology was really interesting and creepy.
Of course, "the" moment of the demo for me was definitely the big reveal of the city. Especially when you see that whale. This is the type of game where I find myself wanting to stop and look at every detail, read every sign. The world that's been created here is really unique and interesting.
Something that surprised me was, I did not expect the enemies in this game to be anything more than zombies, similar to the basic enemies from System Shock 2. I was really happy to find they are actually people, who do all sorts of neat and creepy things (the lady talking the baby cart was my favorite so far).
Was it just me, or was the fire power cool, but a lot less useful than lightning? It just seems more efficient to stun them and kill them, or just shoot them. I'm sure it'll be more effective later, maybe in combination with some aspect of the environment.
Last thing, I do hope there's more of an introduction to the story than we get here. I barely realized I was on a plane before it crashed, not to mention why was I even on a plane? I'm sure this will be provided, I'm just very much a fan of the initial phases of games like these (like in the Half Life games, for example, getting to know the world before it all goes to shit).
But yeah, this will be the first new game I get for my 360 for sure.