Half-Life 2

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You should try Far Cry.  It has realistic physics, fatigue, sniping that matters on position and whether or not you hold your breath.

And you can LEAN AROUND OBSTACLES, thus minimizing your exposure to incoming fire.

Have been playing HL2 some already this week, and I tell ya it's a wild ride. Hopefully Kandrathe & I will be playing it on a sweet DLP projector and some nice speakers, tomorrow night and well into the wee hours. It'll be something interesting to do until the next Guild Wars beta event, anyways. ;)