Just played the demo, and found it pretty meh.
Standing on the train and having to go below the rails to recharge the generators every thirty seconds became boring after the second time, spreading devastation among civilians had no real consequences because of the lack of police/military forces (also... everyone getting back walking aimlessly mere seconds after you blew up cars and killed people in front of them, with you still around? really?), baddies only spawning once you get to some coordinates was downright unacceptable (if you know where they are and try to get them from above - or from behind - then no one will be there, they only appear once you hit some hotspot and this kills immersion completely). When I got to the spot where - I think - fire-powered (the ones that charge and instakill you) baddies first appear, got killed once and couldn't find a way to use the environment to catch them by surprise I got bored and turned the demo off (who needs an open environment when things only happen when you follow a predefined path?).
I liked the intro, explosions and special effects, and climbing buildings, gliding and then falling to the ground blowing everything up with the consequent shockwave was completely awesome, but that's it.
Probably some of my complaints are related to the demo itself (train mission being boring, lack of any consequences for slaying people because of the mission being pretty early in the game, nothing else around except nearly useless power sources), or are caused by the hype surrounding this game (which I can understand, Sucker Punch are awesome) or myself expecting a much different game, but I didn't like what I played.
EDIT: I forgot to mention controls were excellent. You did exactly what you wanted with no difficulty at all, in both platforming and shooting/fighting. Many developers should take some notes here.
These types of things are always fun to watch.
<-- joking. Really. Lighten up.