The only problem I have with this game is that level 39 is damn near impossible on a laptop mousepad. I don't have working speakers, so I can't say anything about the sound, but this game is very cutesy and entertaining. As Otakuhk said, I love that they love falling to their deaths.
I too desire a sell button. Also, please nerf the infestation faction. It really gets on my nerves that I've purchased the Resist upgrade and yet they STILL manage to infest my units 9 time out of 10.
 "Red Remover"){kind=icon}
 "Sonny 2"){kind=icon}
 "Obliterate Everything 2"){kind=icon}