I gotta agree with alot of the votes here, Q3 is one of the best, still give my nod to the original Unreal Tournament (UT99) as being simply one of the greatest FPS games ever made. That was one hella-addictive game!
UT2K4 all the way. What's great is that there are so many mods and conversions, people are still playing it today. It's also probably the fastest shooter ever created...yet it runs smooth as glass on hardware from 4 years ago.
Single player's not the exciting (Halo's is much better), but for value and multiplayer...UT2K4 is one of the best recent games.
With that said, I think HL2's better than either. It's "normal" multiplayer is pretty average, but it's mods are the most played non-MMO games on the PC, period.
comaring halo 2 to ut2004 is like comparing a honda to a bmw (pre-iDrive). there's nothing wrong with the honda, but bmws are better in most every way. un2k4 ftw. nuff said.
Even if you somehow prefer Halo to Unreal, although I don't understand how anyone could, you should be able to find an Unreal mod that you like better than Halo. Here's a list.
UT2K4 was a freakin sweet game. but guess what i get online and there are NO servers up anymore. how good is a game with a horrible gaming community? i love it but nobody else plays anymore. it is extremely fast paced, prolly up there with Q3 arena. great lan game but so old. thats the thing no company is making a fast paced game like that anymore. i can't wait for 2k7 but i wish there were some 2k4 servers up for now.