While we all remember Halo as the FPS that revolutionized the genre in 2001 on Xbox, it wasn't originally going to be for Xbox. Not even a FPS game either. Before Microsoft nabbed Bungie, it was originally suppose to be a 3rd person strategy game for PC and Mac.
Looks really rough, but at least they kept most of their ideas. Master Chief never really kept that mini-gun though. Even though it's neat to see the early shots, I'm really glad it evolved into a FPS. I don't really care for strategy games, and I also wouldn't have some of the best multiplayer games ever made.
I still wonder if Halo had stayed in it's original form if it would have taken off or not. For the people who got to play and see the early builds, apparently the word was positive. Granted some of Bungie's other games are forgettable and it might of landed in the same place. Who knows?