It cool
The plot doesn't really matter here, and moreover it isn't very interesting. Basically you have to recover nuclear warheads from a group of rebels, based primarily in Mexico. Over the course of the narrative you'll hear a bunch of "No man gets left behind!" style chatter from your superiors delivered in a forced, unnatural cadence with no real sense of urgency. But that's really not the point of the game here, it's more about action.
And there's plenty of action online and in the single player campaign. Before each sortie there's a briefing screen through which you can customize your squad of three Ghosts with primary and secondary weapons, as well as grenades. Your own weaponry is customizable as well, giving you the power to attach scopes and silencers to whatever rifles you bring out, swap that in for a machine gun, or opt for a grenade launcher.
Regardless of what you pick, expect most of your team to die, particularly in the last three missions of the campaign. This is the type of game where you're frequently going to get shot and killed by enemies you can't see. Foes can be "tagged," meaning painted with a red diamond, if your squad mates can spot them, but often your buddies won't live long enough to pull that off. Their AI just isn't that good, lowering their already slim chances for survival.