IMHO, a good game with great potential.
I can't listen to the sound so you get my benefit of the doubt ten.
Overall, I really like the game. Chatting with other players can make the game quite enjoyable (or quite irritating in some instances), the multiplayer aspect makes it potentially very funny and gives alot of interactivity imo.
Suggestions:
Upgrading would be all well and good...but that would give other players a leg up....any upgrades should be cosmetic or not game breaking. New armor skins, tank designs, shot graphics, etc.
Make different levels. More variety in the level set up. One gets not just boring after awhile, but it makes it so people like me can figure out great firing lines that only need adjustments in power to hit either position.
All in all....a good game with great potential. Keep working on it.