Windows XP does everything I've ever needed with two exceptions.
1) Good networking with older Windows versions. Plug a crossover cable in between Win 98 and Win XP for example and try to get a network running. Sure you can do it, but it has all kinds of errors. For example its functioning depends on which computer is turned on first, or when one connects to the internet the other constantly attempts to connect as well - until you shut off the other computer.
2) I also want the old methods of working with shortcuts to the drives back. I always have a shortcut to the floppy, hard drive, and CD drive on my desktop. That way I can copy files to wherever I need without opening up My Computer. But in Win XP these are treated as shortcuts and not like drives. For example right click on those and hit properties and you don't get the Scan Disk or Defragment option anymore.