Louis (Left4dead, medical PEELZ guy) armed with uzi
Duke nukem (Duke nukem 4ever, violence-loving badass) armed with magnum
Viktor reznov (black ops, front liner and rallyer of troops) armed with AKS-74u
john marston (red dead redemption, cavalry) armed with Double barreled shotgun
garrus vakarian (mass effect, sniper) armed with M14 EBR
Engineer (team fortress 2, support via tech) armed with frontier justice
and the leader is... (drumroll)
Yahtzee (zero puncuation guy, leader) amed with G36C
the story:
Me: we are at war! you are the galaxy's finest, and we are earth's last hope against the alien psychos!
Louis

EELZPEELZPEELZ i'll be the medic!
Duke nukem: i'll ensure they REST IN PIECES
Viktor: no retreat! no surrender! URAAH!
Mr. marston: "casually puffs cig" let's do this.
garrus:for shepherd!
engy: whoowhee! makin' bacon!
yahtzee: time to kick alien ass!
Me: "pulls out M4A1" are you ready to use these, brothers?
Yahtzee: "loads gun" now i'm ready!
Mr. marston: any last words, mr. Popcarn?
Me: do not pray for easy lives. pray to be "puts on sunglasses" stronger men.
"we load our weapons, then charge into battle epicly"