I find the lack of accurate audio volume and positioning to be by far the most game breaking thing about arma. It simply makes the game *confusing* to hear something in one position but see it somewhere where you would have not placed it by sound.
Positioning of gunfire is especially problematic for me -- I should be able to easily hear the difference between my teammate's rifle 5m to my left and the enemy's rifle 50m to my front. Right now those two sounds are not distinct enough and cause confusion (and frustration).
Playing the first episode of the campaign I noticed that voice positioning is completely wrong. I stood directly in front of a character who was speaking and he sounded as if he were an ambient sound from all directions. Turned left and the audio intensified in my *left* earphone when my right ear was facing the character. Turned my back to him and he was very faint. Turned my left side to him and I heard him in my right ear. At no point did it sound like the audio was actually coming from his mouth.
These kind of things really break immersion, and in some cases gameplay! Please devote some attention to proper sound positioning and volume.