The new iPod Classic is all metal (save for the clickwheel) and feels just about the same as the old classics. It's a little more solid, thanks to the metallic build, but to me the touchwheel feels less sensitive. It shouldn't be, since these are brand new and only been manhandled by a handful of people. The UI is also new—same as on the iPod Nanos—and doesn't really have more features than the old menus on the 5G iPods. It does have Coverflow, which is more responsive than you would think on an iPod.
It's definitely thin. The 80GB model is slightly thinner than the old 30GB, but they didn't have any 160GB models on display. The only thing I have to complain about is that the touchwheel needs a little more sensitivity. Other than that, 80 and 160GB of your music all in one place is nothing to sneeze at.