IMHO, the UI/graphics (and drivers) has always been one of the biggest shortcomings of Linux compared to Windows.
As for the UIs. Between work and home I end up using XP, Win7, Red Hat, and Ubuntu. Red Hat has KDE 3.x, Ubuntu was Gnome 2.x based until the Unity fiasco started. :-( Honestly, they're all pretty good UIs IMHO, some differences, but none stand out as being really great compared to the others. Unity is the most different, buggiest, and worst of the lot. Like I said, bad enough I'm going to switch OSes for no other reason than that. I could slap Gnome or KDE or another window manager on Ubuntu, but I'm just lazy enough to want to run my distro "out of the box" plus it is as good of an excuse as any to fool with Mepis again and a KDE 4.x UI, see how that works. Yes, I realize those reasons are somewhat contradictory. ;-)