Honestly, lack of security and modern DirectX features aside, Windows XP is still a pretty great OS. I use it pretty regularly on one of my retro machines. Granted, I don't have it connected to the internet, and it's certainly not being used as a daily driver. I have mine linked to a shared NAS. VLC is still compatible, so I can watch most video formats. And since I have a GTX 260 with S-Video, I can watch old movies and shows, and emulate old games on my CRT TV, which, to me, is extremely valuable to have. It's a sad reminder that current video cards lack any sort of analog out. Being able to play older PC games without the need for compatibility modes, registry edits and 3rd party tools is a nice thing to have, as well.
Obviously, I don't think I ever would use Windows XP as my daily driver nowadays, more so because of the lack of security, modern features, and support for newer software. But it's definitely a nice OS to revisit, especially if you still have plenty of things you can do on it. Heck, I still do most of my spreadsheets and documents on it, since Office 2010 pretty much has all the features I require. And I sure as hell don't want to be giving Microsoft more money and telemetry than I need to.