I was thinking about the maps that shipped with reach and their inclusion within the campaign. I remember Bungie stating that it was a streamlining process that they didn't want to do again, but what struck me for some maps that shipped with Reach was whether it was really necessary. Take Countdown, Boardwalk and (maybe) reflection. Their appearances within the campaign were trivial at most, and you literally run through countdown and boardwalk, spending no more than 30 seconds there. Creating a substitute environment for the start of Exodus and the launch pad in LNOS would not have very time consuming, and given the visual fatigue that I get with Reach, having a brand environments in matchmaking that you didn't already see in campaign would have helped.
The route that Bungie took with some maps in Halo 3 was also interesting in the way that they are aestetically similar to locations within campaign, but nevertheless they are unique. Take Construct, its literally in the same building as the The Ark, but it does not feel stale. Also, Valhalla uses a lot of textures seen on the Covenant. A similar approach was shown by the background in Epitaph and Isoation, and the use of textures seen in Halo on Snowbound.
