Arma 3 is massive and infinitely customizable, modifiable, expandable and just amazing. It's by far the best war simulator for modern warfare out there and except from the vanilla gameplay you will also find an endless list of mods and assets out there if you want advance your gameplay with even more awesome content. I'm soon reaching 4000 hrs of this game and I still learn new things every time I play this game. You also need a serious PC (INTEL CPU) to run it well.
ARMA is not a 'run and gun' game to be honest, so no matter what first person shooter you're 'god' in, ARMA will have you start at ground zero, with all the rest. Generally the player maturity level in this game is much higher than any other games out there so you will most likely meet adults when you actually play the real game itself and not wasting your time on a roleplay server where all the children stick to.

I 10/10 highly recommend this game due to the realism and massive content this game has.

This game takes away my social life, is it worth it you may ask? Hell yeah I'd say!