During Nexuiz 2.4.2, I could recall seeing at least a couple hundred players online every time I booted the game up. Jumping into grapple hook CTF normal weapons matches was only difficult because the servers hosting it would always max out. It wasn't in the mainstream, but for an underground FPS it was damn popular. Sadly the game was in a slow decline up to the point of a certain event happening and said event was basically the death of it. Xonotic for whatever reason never gained Nexuiz's playerbase back either, though one could hope it some day does.
ECKZBAWKZ HUGE LIST OF ACHIEVEMENTS GOES HERE....
Oh wait.