It is THE game to play when it comes to war game simulators.
Atmosphere:
Arma 3 is exceptionally good for its atmosphere, giving you the feeling of actually being there, in the middle of a war zone, fighting with the enemy. There are 2 maps and both are huge, taking quite some time to travel from 1 place to another, especially on foot. There are also a lot of mods that add to the experience.
Gameplay:
It's engine might be lacking a bit (also could be a huge resource hog, especially on the CPU), but it makes up for that by giving you a unique feeling when it comes to war games. It is unforgiving, and every mistake you make will have its consequences. It has enough vehicles (sea, air, land) to keep it interesting and a large variety of weapons you can choose from.
Graphics:
Graphics are excellent on some higher settings. Sadly this is when hardware steps in. The game is EXTREMELY demanding (as i have mentioned in the Gameplay section) and will make your PC beg for mercy on the highest draw distance and some form of better AA, but that is to be expected from a game like this with no load times and a huge terrain.
All in all a great game that i would recommend to every fan of war games!