the demo is actually pretty clever. It's basically several very different parts of the game glued together to make it seem like one level.
That's one thing that I wish other developers would copy. Monolith did this with the original FEAR and Condemned, good way to show off the game without wearing out any one area.
yeah, it was actually about 4 or 5 vastly different areas of the game put together. One lame thing about it is that mech battle from the demo is
spoiler (click to show/hide)
the second of two mech scenes. I remember them talking about how the mech scenes would be pallet cleansers, but it's more like: after every third of the game, enjoy a boring mech sequence that lasts 3 minutes.
there are other small changes from the demo too, like they don't give you the rocket launcher in that area in the full game to make the fight against the laser guy really easy (unless you were well prepared and had one handy). Another odd thing is that the only area in the entire game that has stuttering is that outdoor demo area.
oh, and with the exception of the very beginning of the game, there aren't as many "scary" stuff as the demo would lead you to believe, usually they're brief and spaced out to now get too annoying.