Has potential. The audio levels should be tweaked, imo. Louder speech, quieter ambience, just so the voice can be heard without having the neighbours hear the background music.
1) Not enough coins per kill. 2) Trying to hit something is frustrating unless it's coming straight at you. 3) Most towers are totally useless because a) you can't upgrade them later on; or b) you can't afford them (i.e. the modifier towers)
Font is hard to read; damage display bugged (my guns don't do anywhere near enough damage to kill the creeps as soon as they spawn...); mute doesn't mute (wouldn't be so bad if the sound effects weren't as annoying); upgrades display shows upgrades past the maximum attainable.