Playing the Unreal Tournament single player campaign (with bots), it's quite great actually.
UT has some of the best atmosphere of any game I've played. Certainly of any arena FPS, by a very wide margin. Also love the worldbuilding you get in the character bios, map descriptions and visual design - it somehow becomes an immersive sci-fi universe. By the time you finally face Xan, the hype is very real.
They completely dropped the ball with all of that in UT2003. I like its more defensive and movement-intensive gameplay, and IMO it's a better online game than the first one, but there's basically zero atmosphere and the worldbuilding isn't played seriously or consistently.