The large room sometimes causes your game to be choppy (espeically on split-screen) so be wary. Upon entering the convention hall, you can simply picture yourself shooting up E3 (or CES). On semiautomatic, an accurate assault rifle will be able to take down enemies not under cover only the lack of penetration will be your primary problem with this set-up. If you do take a light machinegun, be sure to take along an accurate assault rifle (the G3KA4 is a good choice if you have unlocked it, since it's used by terrorists here) and a 6X Scope. You can do so for this act, or at least until you are at the Monorail Station.
However, the first two areas of the convention hall are more suited to medium range fighting - if you have a light machinegun you've been dying to use, take it out and go loud and messy. Outfit your character the same way if you like. You can use them to re-equip your character if you missed doing so on the chopper ride in. For some strange reason, there are supply crates on the rooftop.
