I'm not going to go into any great detail, seeing as I could write pages on this stuff.
But the jist of it is I'm fine with WinXP, because, well, it works. I'm also a gamer, so I need at least WinXP for DirectX. The one thing that really gets me about WinXP (or any other NT kernel) is how much they love to use services, and the sheer amount of useless ones that are enabled by default.
The problem with every MS OS before it was that they all sucked... hard. The 9x kernels were all complete trash, and NT4 was a pain. Now adays things are abit different. Vista I'm not touching until at least service pack 1, and only will I get it when I really want to play some DirectX 10 based games. I wouldn't have done it a few years ago, but with the advent of Mac OS X, I'd recommend Mac's to any normal desktop user who asks me what new computer they buy.
"With out walls and fences there would be no need for windows and gates!"