Beware the smiley face! =D
Now, I dont really know for certain who the main character will be. Probably Chief. But it could be Spartan-259.
So if he ISN'T the main character, or even if he is, there could be another bonus for completing
campaign on Legendary. The bonus could unlock a bonus level from another Halo game, or a mission we would have liked to have had in another Halo game?
Possibilities -
The Maw from Halo CE, but so people who have this as their first Halo game are not completely confused by the cutscene sections of it, you just have a replica of the warthog run (Including Foehammer crashing and the huge jump) And then the final cutscene where you fly to safety.
Pillar of Autumn from Halo CE. A slight continuation into Halo Combat Evolved.
Masterchief (And dosen't he find other Spartans in a book or something?) on their way back to Earth after Halo CE. Also, it could reveal how Johnson mysteriouly escaped from that giant hula hoop.
EDIT - One more thing is, as its more likely Reach players will have played Halo 2 than another Halo game except 3, is a level where you are in the Forerunner ship (Transition from Halo 2 to Halo 3) If the Covenant are flying it, surely you will encounter some opposition by throwing yourself inside on launch?
[Edited on 08.04.2009 9:43 PM PDT]