If you enjoy tactical shooters Insurgency is hands down the best fps out there currently. Not as demanding as ARMA, meaning you can jump in and play a round or two as you wish and not as arcade-ish as other shooters out there, meaning no huge HUDs or kill messages and rank ups. If you have some friends to play with its even greater. Its like a mix of Counter strike and Project Reality.
Some extras
+Weapon customization (scopes, heavier barrels, flashlighs as well as full kit setup with more ammo pouches and heavier armor or not)
+Leaning
+Realistic sounds and effects (bullets wheezing and cracking above your head sound changes depending on indoors or outdoors or suppression effect active)
+Effects after running on your aim
-multiplayer only which means there is the fair share of fucktards and that it may have limited lifespan.
-Really wish it had Mumble instead of the shitty voice system it currently has.
Overall 9.0/10