I played the demo on the 360 last night and I hated it.
But I just finished the demo on the PC and loved it. I guess I'm a L4D-PC only guy. I love the characters. Funny, clever and just as good as the first set, I'd say.
I feel like these characters are more realistic though. The first four feel like they were cartoonish, but these just feel like real people, you know? XD