Without doubt ArmA is a great simulator.
You need patience to finish all the missions, principal and auxiliary because they are very hard and you need to repeat them many times until you get the right tactic. The graphics aren't extraordinary like Far Cry or other exotic games, just right for a tactical-simulator-shooter, but you need a good system. At the time the game was released it had a lot of bugs but with the time the patches fixed this problem.. and the Editor option make this game customizable and become immersive. A good thing the producers did..