Heavily scripted shooters that take place in glorified corridors are well and good for most, but some people like to kill things out in the open, and kill them with a single bullet. For them, there is ArmA series, and for them, a third game in the franchise is on its way.
ArmA III expands on the same basic premise of the last two games, in that it takes place on a large island and gives you access to every inch of said island, along with the ability to do anything from run around shooting a pistol to climbing in a chopper to driving a tank.
In addition to a singleplayer campaign, there's the expected multiplayer modes (with both "cooperative and competitive scenarios") and mod tools. You can also create dedicated servers on both PC and Linux.
It'll be out next year.