Meh... I'm actually a fan of XP's design, although I can't tell how much of that is actual aesthetic appreciation and how much just nostalgia. Colors are nice, yet the interface as a whole was actually less flashy than its successors, as the last pre-GPU-compositing Windows, making for a solid whole. But I also liked Aero's glossiness, which I'm happy to see somewhat reflected in Yosemite - nor did I ever have an issue with OS X, although iOS 6 was a bit much for my taste. (On the other hand, I also like iOS 7. The only design I seriously don't like is Google's, for reasons I'll elaborate on the off-chance anyone cares.)