Bungi also had worked on Marathon which was apparently a really popular Mac game, so I think they also drew from that franchise aswell.
Halo hasn't done anything that innovative, but instead takes elements from many great shooters and tweaks them. In the end, it all comes together like a massive puzzle. Great story, great gameplay, great graphics, great cinematics, and great multiplayer to keep you coming back again and again.
However, I also can't wait to play Metroid Prime 3, which will be my first 3D Metroid game and sadly the last Metroid game there'll be, but it sure looks great and original in every way, so that makes up for everything.