It's basically a giant iPod Touch. There really aren't any extra features, other than the fact that it's a lot more technically capable.
Yeah, it doesn't really make any sense logically, but it's really, really cool. I went by the Apple Store today and played with one for about an hour. It's ridiculous just how cool and fun it is just to mess around with. It's like that feeling you got when you first picked up and played with an iPhone, but five times better.