I've heard that SOCOM is pretty awesome (not available for mac) and there is a story relating to one of the commercials about that game, remember the one in which they're playing online and this mysterious group signs into the game and methodically blows everybody else away and all the "dead" players wonder: Who ARE those guys? And it turns out to be a REAL SEAL team playing on a laptop in the middle of the desert? Well, I had a buddy at SOCOM who recently retired as an 05 and he said it really happened! "Just like shootin' fish in a barrel..."
I like the Clancy games (wish more were ported to the mac) because his company employs ex SpecOps guys to write the tactics and so I have a chance to use my own experience and training in the mission planning and execution phases. Works pretty well with Ghost Recon and Rogue Spear. Weapons capabilities are extremely realistic, too.