ArmA's visuals are good and fit the game, though they really don't stand up to other games currently available on the PC. At the same time, ArmA's scale earns it leeway. Environments are huge and filled with small details that sell the realistic feel. Areas rarely feel like they were planned out - at least when compared to more linear shooters. One of the few downsides is that the visuals are inconsistent. Some characters and vehicles look great, while others don't. Obviously the game looks its best with all of the visual bells and whistles turned up, though this creates some framerate issues.
Voice acting is generally good, at least during story sequences. Radio chatter doesn't sound great, mainly because it was obviously pieced together using separate pieces. Other than the spotty radio chatter, everything else sounds great. ArmA is one of the few games on the market where you really get the impact of bullets hitting around you or whizzing past your head. All audio is positional, which helps when trying to determine where you should go next or where the action is. Background gunfire isn't just for effect, but a signal that a battle is going on nearby.