I'm up to level 9 now. Been messing around at the ball throwing game and still trying to go beyond level 6.
The demo is rubbish, it's not indicative of what the actual game is like at all. Granted, it plays the same, but the full game has a great storyline and brilliant atmosphere, whereas the demo just makes it seem like a shallow and rather awkward "zombie/alien dismemberment game".
Yes you are right. I remember trying out the demo when it was first released, put me off completly till a year later and realised how awesome the game really was.