Love the demo on the whole.
The graphics, voice acting and dark and grim feel of the game are all brilliant! The combat system is as good as you're gonna get, really. Although it could feel a little heavier, as in making you feel the impact of Batmans knockout blows. But the way batman leaps from person to person, taking them all out in 1 giant combo is great.
Someone mentioned on a previous page that it plays a lot like batman begins on the older consoles. That's bang on. It does. It put me in mind of Begins the most when you are perched high up in the rooms, taking out enemies silently from above. It's just like it.
So as good as the gameplay is, it's definitely not anything we've never seen before. Nothing really blew me away about the gameplay. I reckon this is where reviewers might knock the score down. What did blow me away about the demo was everything else! The graphics, feel, characters, etc.
So yeah, I love it. 10/10. There's nothing wrong with the gameplay, just seen it all before.