UT 2004 is a very good game, like the old UTs. You have many different kind of games (capture the flag, domination, deathmatch, assault, ...). It's very easy to play online with other human players. You can have also a lot of fun playing alone by configuring the AIs the way you want. The gameplay is excellent.
If you like FPS, this game is really good. There is no story and you can play just 5 minutes when you have finished your working day