I say go for a character with a voice. Cut out the stereotypical macho bullshit, and give me a character with even a shred of the tenacity and fucking brilliance Jack Bauer (and Keifer Sutherland on the whole) exhibits, and you've got yourself a winner.
Perhaps have Deus Ex style conversation trees, such as below:
Player: "Chief, I need some ordinance here ASAP, the area is hot"
Chief: "Alright son, you've got it, what do you need specifically?"
Player: "I need..."
A) a weapon and ammunition drop, I'm running low/don't have the equipment for the job.
B) An airstrike at this location
C) A chopper to take me above the city, I need to clear the rooftops; they're positively crawling with Tangos/Charlie/Communists
And so on, give the player a choice in his actions and allow his choices to be represented with sharp dialogue and a fantastic voice actor.
