It depended to some degree on which branch you reached XP by:
1) From Windows 95->98->ME as a consumer
2) From NT3.5->NT4->W2000 as a professional
In the former case you lost quite a lot of DOS games and win16 support, but gained much better stability and security (yes, I know pre SP3 XP was hardly great, but compared to 16-bit?!)
In the latter case you got...few more devices supported and a Fisher-Price interface? Oh yes, and "product activation". But at least you could go for classic look and be back like w2k (as I did). Having said that, all that w2k effectively gave me over NT4 was USB support really.
Due to product activation, and some other reasons, w2k was last Windows I bought, XP came as work system. Now I am using Linux almost exclusively and my old w2k & XP machines run as VMs on top. Critically the license for them allows that, something the consumer versions of Fista & Win7, etc, do not.