One interesting change I discovered in XP SP2 was that Subspace Continuum -- the first and (by far) best massively multiplayer online game -- now runs on XP without entering an infinite loop trying to launch the process. This only repro'd under certain accounts, and I suspect it was a bug in their anti-hacking/cheating code, but SP2 seems to fix the problem.
Well, what are you waiting for? It's free! Start playing today! I can sometimes be found as “IUnknown*” in Alpha West (I'm a perpetual newbie). Mention that you saw my blog and I won't kill you. :-)
[Edit: Speaking of great games, here's a remake of Lemmings in DHTML! Very cool, I wonder how long this link will last. What ever happened to Psygnosis? Their games for the Amiga were excellent...]