1) With a single button press, one can activate the Rookie's VISR mode (Visual Intelligence System, Reconnaissance), which makes everything look all Tron-y.
I dig that.
2) Yes, the single-player in this so-called expansion pack is short, but roughly the same length as Call of Duty 4 and Halo 3. Unfortunately, once you realize that you can run past the enemies in the Rookie's open-ended segments, the game can be completed in only two or three hours on standard difficulty. There isn't much to explore in New Mombasa, and the level design and encounters grow monotonous after an hour or two of play.
3) Halo 2 and Halo 3's segments on Earth were curiously free of civilians. This was understandable in Halo 2, due to limitations in the technology and the fact that the Earth had just been attacked, but it was one of many factors that made Halo 3 lack the dramatic punch that a series' finale should have had.
This time around, it works to the game's advantage. Wondering the empty streets of New Mombasa sets an nice tone for the rest of the game, both moody and haunted, certainly the stuff that noir stories are made of, but...