My only complaint is the music stops the moment I click outside the game, meaning I can't have it as background music. I would prefer if it continued and simply had a mute button.
The only thing I didn't like was that you couldn't change weapons on the towers after you had upgraded them, which wasn't very fun for me when an area kept getting attacked and the tower in it had machineguns :/
I beat the game before badges were added and now when I return I got the easy and hard badge but not the medium ones, meaning I will have to restart the game if I wanna get the Boss Badge. Though I cant do that because for some reason I suddenly need to update my flash player to play this even though I played it before.