- last post: 01.01.0001 12:00 AM PDT
Another vote for Outskirts. Any level past that would give away too much of the plot.
SPOILER
In Metropolis, if I remember, you essentially take down a bigassed mechanical spider (also known as a scarab). The Silent Cartographer in H1 sorta gave the player a taste as well as building anticipation for what the rest of the game would be like. Essentials like The Flood or Monitor were kept well hidden by that time.
Delta Halo would reveal to the player that there is another Halo...remember, if you never played H2 before (I'm sure the rock you live under is lovely, by the by), it'd suck if half the game was introduced through a level that included the Arbiter or Delta Halo. Each Halo game seems to have some hidden secret somewhere along the line; in H1 it was The Flood and the revelation of why there was a gigantic ring floating in outer space, in H2 it was Delta Halo and (UBER SPOILER. You've been warned) being able to play as a split-chinned Arbiter Elite.
[Edited on 1/2/2007]