Later. It's late where I live.
I also don't play many shooters. Although as someone who didn't enjoy bioshock because as awesome as it was, it wasn't fun, I would say Halo is in many ways the best FPS I've ever played, and in some ways simply the best FPS ever. Especially considering it's the best multiplayer online shooter I am aware of. I'm all about the multiplayer, and made an exception for the original Halo campaign.
Part of why I consider it the best though is that it is the first and last online FPS I was willing to get good at. Something about FPS's simply makes them too complicated for me to be willing to learn the subtleties of more than one. I think it might have something to do with the control scheme, but I won't be sure until I play the conduit.
In short, I am biased partially because Halo is the only FPS I was ever willing to get good at, possibly because it was my first. All the other FPS's were too complicated, considering I was already good at Halo and didn't feel a need to learn another control scheme for any FPS ever again, as learning every new control scheme to the point where I was adapt at multiplayer just was not fun. Well, except Metroid Prime 3, but that game doesn't have multiplayer.