You never played Starcraft or Warcraft? How about Red Alert or Age of Empires? You basically have a "base" and you build units to send off to kill your enemy's base. It isn't an FPS in the slightest.

There is, however, a new FPS Halo game coming out as well. I can't remember the name of it, but it was in the december issue of Official Xbox Magazine (which I highly recommend you guys subscribe to.)