The Batman game is freaking awesome. The demo is short, very short, and doesn't do the full game justice. The demo actually uses a few different areas from the full game to make up the demo. What you see isn't what you get, so to speak. If you play the full game however, you'll get hooked.
The demo also doesn't show you that you get to upgrade aspects of Batman and his various abilities/actions/weapons.
The story is amazing, though. Visual presentation is 10/10. The Scarecrow is FREAKY AS HELL. Audio is 10/10 (it does native 5.1, so if you have it.... well, you'll hear it. :-D). Harley Quinn is 20/10. :-P Controls on keyboard are annoying, yes, but use keyboard for movement and mouse for attacks/actions and you're gold.
Personally, I found the quality level of this game to be very unexpected. I vote it game of the year, easy.