lets see... um you are a part of a six man team known as the ODST's (Orbital Drop Shock Troopers), and you crash land in the African city of New Mombasa. In New Mombasa there is a Super Intendant, he is a Very Powerfull AI unit but has been damaged durin the assault of new mombasa, as you walk around he helps direct you on the right path, and you keep finding objects that will flash you back to your other team-members, ummm lets see... my guess is that the odst's eventually help the Master Chief, and save New Mombosa, (Not Shur about that last part.) but the HUD is Extremely awesome when its dark you can push a button and it outlines EVERYTHING, its really cool. another thing is the ODST's pistol is like the one in Halo 1 where its really overpowered. thats all i can think of right now. i dont think youll get much more than that unless you talk to a hacker or a shifty BUNGIE agent...... I even went to the PAX and thats all they give out....
Hope this helps, let me know how it goes