Fun Game ^.^
The Defense mode was fun. Basically, it starts out kind of difficult, but if you use your EXP correctly, you can get ahead of the game and have a lot of fun just ripping through the levels with ease for a good long time. I quit playing after reaching just above 3,000 kills, where I had most of the guns, all the power-ups, and over 3,000 hp and base hp.
My only complaint is that the sound sometimes got behind the guns (you would fire, and the sound would come a second or two after).
Loved the game! Keep it up.