Although controversial, especially in that the campaign is said to be released as a free DLC in later versions in lieu of including it in the formal released version, I nevertheless consider ArmA3 as a masterpiece.
In ArmA3 CQB is smoother, collision is more realistic, and mission editor is even more usable. It absorbs several advantages from ACE2, which is a modification of its former work, for instance, AI is able to lean their bodies, and you can switch the optics on the rifle. Successive adjustment of body position is cherished, as it allows players to take advantage of covers better. The introduction of penetration system makes the game step further towards military simulation, and if one is extremely interested in experiencing realistic ballistic system, one should never miss this game. Generally, ArmA3 is a great advancement of ArmA series, and no one can deny its eminence and outstanding performance in military simulation.
But ArmA3 is still far from being perfect, in my point of view. Sometimes I feel like I am splashed by some water drops rather than hit by real bullets, in another word, the hit effect system is atrocious. There are few bugs urged to be fixed, sometimes I can even move through a wall. And the exportation of missions in the editor sometimes leads the mission file to be damaged.
In addition, from the aspect of optimization, I sincerely hope that ArmA3 is able to support RAM over 2GB.