GameSpy: How important is lighting for building a successful level?
Tyson Green: To a designer, lighting is a tool to control mood and influence the player's state of mind. Sometimes, more dynamic use of light can be used to put a twist on an encounter, but this is uncommon on the scale of an entire level. So it is possible to design a mission without worrying too much about light (beyond that which is needed to see), but the mood might not be that interesting.
GameSpy: Will we be seeing different types of levels than we saw in the first game, layout-wise?
Tyson Green: Definitely, but I don't want to spoil any of them.

In general terms, though, we were able to pull off some much grander environments in Halo 2, which let us try some novel layouts. Halo was mostly corridor crawls and vehicle canyons, which is something we were able to avoid this time.

GameSpy: It seems that the single player levels in Halo 2 are much larger than they were in the original game. How was this acheived?
Tyson Green: In large part by greater experience with our engine, more pervasive use of vehicles, and a few bits of new technology.

Part of it, though, is that the missions in Halo didn't need as large environments. The capability was always there, or close to it. We've simply exercised it more in Halo 2.
GameSpy: Do these larger levels allow the designers to do different things with the gameplay mechanics?
Tyson Green: They allow us to have some larger dynamic elements, certainly.

However, the situation wasn't that we suddenly found that we could make larger levels, and that this opened up a bunch of possibilities. It was actually the other way around. Since we wanted to do things that called for more space, like vehicle encounters or Banshee dogfighting, we made the levels larger.