UT 2004 remains the best and most supported (in terms of mods) fast-paced shooter. It stands easily shoulder to shoulder with counter-strike, TF2, CoD4 and BF games.
While Quake III might still be the last word in fast paced shooter, UT2004 is the first word.
Getting the game at this price from such an outstanding download service (even better than steam!!) is a steal.
I recommend this to any lover of the FPS genre- it's a nice contrast to the TONS of tactical shooters around now.
So chill out, and have some funtime with UT2004!