Even if it is just one level I really like the game and can't wait to get more :). I can fully understand why you couldn't add more levels, as I can imagine that adding the core mechanics for this game is already quite a lot of work. Your graphics are also perfect for this game!
The only thing I didn't get is, why do I win the game if they still bombed 1 of the two sites? I think preventing the bombing of all three sites is not possible, but still I was wondering about that.