PvK, what changes in XP user interface were you talking about? For me, XP looks almost like 98 after a few tweaks (removing the horrible basic interface, disabling Messenger and so on). Of course, with the basic interface, I can understand your problems.
As for old games, it mostly depends on the game in my experience. While Daggerfall runs like a charm on XP (yes, I even managed to play Daggerfall for several hours without a crash on XP), I have quite a few games that refuse to launch when they don't basically crash the whole system. But I would believe the same can be said of 2000 as well.
If given the choice, I would gladly go back to 98SE as soon as possible, as this OS is much simpler and less cumbersome. (And my computer is a bit slow to run XP with ease as well) However, I don't have the Second Edition of 98 and cannot find it anywhere, so I am basically stuck with XP since 98 (first edition) is lacking connection sharing. Either that, or I couldn't make it work, your choice. And I don't recall having much issues with stability back in those days when I used 98 either.