Nothing directly Halo-related here, but there's an interesting interview at GamingGroove with Tim Sweeney of Epic Games. One of the topics mentioned was the balance between art creation and programming in games, and how emphasis is switching from the latter to the former:

Art requirements are going up dramatically with the coming generation. The content we're building in Unreal Engine 3 looks perhaps 10 times better than in the previous generation, but it's taking 3-4 times longer to model such high-polygon objects. Our art requirements are approaching what you see in movies; they are perhaps a factor of 4 lower right now, but in the two previous generations our detail was tens and hundreds of times lower!

Food for thought when wondering where the three years it took to make Halo 2 went: there's an awful lot of detail in there.