You are a mercenary in small Latin American country during a revolution. Your main contract is to hunt down Russian businessmen, and while doing that you will eather protect the govermnent or help the bunch of bearded men with Kalashnokovs to take over the country.
Well, this is not a new game. In fact, it was released in 2009, so don't expect up-to-date graphics. Its gameplay is what makes this game unique. It's the most realistic tactical simulator in the world. The closest example is new JA.
Second strength of 7.62 High Caliber is guns. There are tons of guns (pistols, assault rifles, shotguns, smgs, machine guns, rifles, sniper rifles) and lots of attachements (scopes, colimators, laser sights, flashlights, grips, grenade launchers).
So, if you are looking for realistic tactical simulator with enormous range of guns - this is the game.
P.S. I would also recomment checking out Hard Life and Arma Realista mods. Hard LIfe makes game more varied, add more capabilities; Arma Realista makes range of guns more authentic for Latin American region (how about 20 types of AK and 15 clones of Colt 1911?)