Black Shades
(http://cdn.wolfire.com/images/bs/3.jpg)
(http://cdn.wolfire.com/images/bs/2.jpg)
Nothing terrificly special, but fun and quite addicting nonetheless. Very basic, fast-paced gameplay.
You are a bodyguard for the President. Use the weapons (or lack of) at your disposal, as well as a time-slowing Matrix-esque reflex ability, to protect the President from assassins. Advance through progressively harder levels and see how long you can survive. (Oh yes, and there's zombies.)
Like I said, it's pretty basic, but it's rewarding when you take out that armed assassin just in the nick of time or throw the president out of harm's way right as a bullet flies by his head.
Main site (http://www.wolfire.com/black-shades)
Download for Windows (http://cdn.wolfire.com/games/BlackShadesSetup.exe)
(Also available on the iPhone.)