It's no surprise, then, that one of the big changes in Halo 2 is that there really isn't very much repetition at all, and this is due mostly to the hard work of the level designers. We recently got a chance to ask Tyson Green some questions about the single player game, and he had some interesting things to say about the nature of the occupation.
GameSpy: How important is level design to creating a cohesive narrative?

Tyson Green: Important on the large timescales, where you design with a mind to pacing and even distribution of story events, but not very important on the shorter scales, where you're worrying about how a room is built or an encounter plays out. On the small timescale, it is more important that you don't ruin the narrative by competing with itit is hard to tell a story to a player who is busy trying to repulse an attack.GameSpy: One of the complaints many people had with the original Halo was that there is a lot of backtracking, or repetitive parts of many levels. How important was it to you to create levels that weren't repetitive?
Tyson Green: Very important, but in Halo, it was also important to ship more than five missions. It was unfortunately a matter of choosing whether to have that repetition, or settle with a much shorter game. You have gangrene, do you want to cut your hand off, or your entire arm? Not a fun decision to make, but I think we made the right one. On Halo 2, we managed to avoid being backed into that corner.GameSpy: How did you actually go about ensuring that they wouldn't be? (repetitive, that is)
Tyson Green: We simply made sure we had enough time, and were better at cutting sections that turned out repetitive anyway. Repetition isn't something that happens by accident and surprises you, it's something do you if you're hard up for time, or if your environment calls for it (a tunnel, for example, isn't going to exhibit a lot of variety by default).