Ok I'm very impressed with this demo, has to be the first game that's truly shown how good the PS3 can be when a game is developed fully. LBP was also great but that's a entirely different style of game. So glad I bought my new AV receiver last month, the surround sound in this game is awesome.
Aiming was my usual hit and miss affair but that'll improve with time, I like that nearby explosions etc unsettle your aim. Good frantic gameplay, lots going on. The enemy AI appears to be of a high standard.