When I want realism, I'll play ARMA 2 or Flight Simulator.
When I want fun, I'll look to Duke Nukem.
When I want senseless, brainless, mindless, thoughtless shooty gun play, I'll look to Call of Duty 4...and then turn quickly away and look back to Duke Nukem.
Even though it may not have the heart it once had, and the game play may be extracted from Halo and Call of Duty, I play it for Duke. He's a parody of himself, and I enjoy laughing along as he laughs at himself. Better than smug super hero soldiers running dumbfoundedly into the middle of a firefight yelling all that hollywood take-cover-shoot-them-grenade-exclimationpoint-get-to-the-choppa gibberish. But that's just me.