Simulation: toss up between ARMA 3 and DCS FC3.
General game: Bioshock Inf., Borderlands 2.
RTS: Rome 2, Wargame Air/Land battle.
ARMA 3 can be amazing at times, I've had some pretty interesting fights in buildings near cliffs with 3 other friendlies and dozens of enemies assaulting our positions, with rounds constantly cracking around through my surround sound, that makes it the most immersive game I've played.