Yea, buy it! There really isn't any other game out there that provides the diversity in game-play as UT2004.
Ironically, this very diversity is leading to the lack of on-line players.
I know it sounds strange, but consider when you give one group of children 10 toys to play with and another group just 1 toy. The group with 10 toys will rapidly loose interest in the toys, while the group with 1 toy will cherish their one and only toy.