Ever so slightly slimmer (again)
12 hour battery life, up from 8 - much needed improvement, could be better though
new scroll wheel copied off the iPod mini - not a huge deal
UI changes - Minor tweaking that could have been done to existing models
20 and 40gb - Still has the Karma beat for size, and the high end iPod price spot sits empty, awaiting the 60gb versions.
For me, 40gb would probably be about what I could squeeze my music onto. The Karma's 18.6 gb usable space was difficult, and so my Europe trip music has been lacking a few albums I wished were on there.