This is a very nice looking game. The controls felt awkward until I realized WASD moved the tank as well, then that was good too.
The lack of sounds isn't too bad, but there should definitely be some kind of background to fill all the silent portions of the games. The effects you do have are good though.
The gameplay is pretty good but I agree with other comments that there's a lot of backtracking and just getting through boxes, which feels more tedious than challenging.