Halo is a PC FPS. I don't care if Doom III comes out on Xbox first (
), it's still a PC FPS. Bungie was developing it for the PC long before they were bought out. It was designed to be played on PC, just they had to change things up for the controller. It's still a PC FPS, no matter what.
It's like Splinter Cell, it's a PC FPS, but it'll be out on Xbox first. Still, it's a game meant for PC, part of a PC series, and that's what makes it a PC FPS. It's no Metroid, TimeSplitters, GoldenEye, or Turok.
And Halo is being redesigned to take advantage of the PC platform. And if it's more than just a port with added online features for PC, you know they messed up the game quite a bit bringing it to Xbox.