I think what sets Halo apart from, uh...other sci-fi FPSs? Wait, how many of these are there? I guess Unreal is one...Doom could sorta count...and AvP...? I guess I'm out of the loop, idk...Well, anyways, what sets Halo apart from whatever other generic sci-fi FPSs that are out there is attention to detail & balance. The story is good (if you care to pay attention to the canon there certainly is a lot of it) and the music matches the epic, alien landscapes. Add to that one of the largest communities (one that Bungie actually pays attention to! *shock*) and you've got a very solid FPS franchise. I also played the demo for Halo Wars just for kicks and actually enjoyed it (though I only played the first level) which is saying a lot because I UFCKING HATE RTS!! But that's besides the point...
I'm sorry, ZombieBucky, but Tetris is clearly a commie conspiracy...I'll stick with lame ass Bejeweled. >_>