Hands down, there is not a more expansive, open world military simulation out there. Save maybe America's Army 3. Though there are missions which are very linear, there are also many missions that leave it to you to tactically out-think the AI, which isn't that bad. It's not that smart, almost like out-maneuvering an 8th grader (though sometimes it seems entirely more smart than it should be) but when it comes to fire-fights, you best bring a med-kit., because it's going to get bloody.

If you ever wanted to fly an F-35, Apache or Cobra or Hughey, hitch a ride on an M3 Bradley, ride a mountain bike through the hills of Chechnya (or wherever it is) to hook up with an Osprey, hunt down a suspected terrorist in an Eastern Block village, or any other number of interesting situations (such as getting your ass fragged by a nuke in some 3rd world country and having to fight your way out of bat country), this is the game you want to engage with. Only complaint is the voice overs.