I've been using a 2.5.2 dev build for a while, and now just upgraded to final version. I downloaded the patch and extracted it to my Nexuiz directory as usual. Launched the game, and there's nothing in the singleplayer window. Can it be because I should have patched 2.5.1 instead?

E: I see many people have problems with the patch. I guess I should just do a clean install.

Yes it would be a good idea to switch to the full version, however, you could probably fix this just by removing the g_campaign cvars from your config.cfg file. Then it will load the defaults and should show the new campaign.