So I just finished the demo, and....
It's not that bad.
It's not spectacular, but it doesn't suck.
The cut scenes are underwhelming after MGS4, but that was to be expected. I'd say the cut scenes are no worse than the cut scenes from the Halo series... not that that is saying very much. The script is a bit stilted. The voice acting is decent considering what they have to work with.
The graphics are ok, slow frame rate. I struggled with the camera until I realized you can change the camera angle with the d-pad. I suggest setting the camera to "back" so you don't have to baby sit it so much.
The gameplay is... well, I honestly never felt like I was in control of my character. The combat is slow. But I'd be interested to see how this develops as your character levels up. This game doesn't seem like you can really get a feel for it with a demo. They should have given you a demo that levels quickly or just given you a tricked out character to play with for a while. I can see how I'd really dig the game after getting into it and playing with a friend.
Hard to be super excited about this game right now. I wish it were four player co op. I'll probably at least rent it and do some co op with ferricide when it comes out though.