It's still Vista, sure it's a little faster now but essentially it's the same product. Games don't work very well and older applications don't function correctly even with compatibility modes. A but coerced improvement is the ability to choose your browser on install, but only in the european version. You still have to restart the whole computer over and over again while making any slightly more administrative tasks. UAC is still a pain but on the upside it's easier to turn off (but not without restarting... again). Aero doesn't work with alot of windowed to fullscreen applications which was a major downside for me personally. The boot up time is still slow as ever which makes for even more annoyances. The bulk copying of files is ever so slow, I don't understand how they've yet to improve upon it. If you are happy with XP I see little reason to upgrade.
Faster than Vista
Games don't work properly, especially older ones
Upgrading/migrating takes longer than expected