This was a good game, yet I found it was still lacking. You see, I didn't feel satisfied when I beat the game because I didn't get to use all my upgrades. What's the point of having three level upgrades when you pretty much beat the game within two? I think you should make the route to China a little longer and harder as I progress so all my stuff wouldn't be so overpowered.
Also, please test and fix the game so that people get to the other side at the nick of time. That usually happens in games like these but this doesn't have that part.
The spawn frequency of the moles should be lessened.
The drill should be constantly purchased in order to use. Sort of like the bomb.