The protagonist of Valve's Half-Life series of games will be making an appearance as a playable character in Renegade Ops, a top-down action game that's very much in the vein of Jungle Strike, Seek & Destroy, and Return Fire.
The Steamworks version of the game will offer players the chance to take the wheel as Gordon Freeman in the Half-Life buggy while utilizing a host of special weapons, including Ant Lions.
Renegade Ops offers both a single player campaign and a 4-player cooperative campaign and is currently available for pre-order on Steam. It also supports split-screen co-op if you pick it up on the PlayStation 3 and 360 where it's currently available.
The game is currently in development at Avalanche Studios and uses the same engine as their other game, Just Cause 2. If that's not reason enough to play the game, I don't know what is.