From my last comment, as in, if I got 1000 kills in a period of 5 hours, I would not be rewarded. If I got 15 kills in a matter of 20 seconds, I would. This is the only game where 15 kills can be better than 1000 kills... My suggestion is count rewards with points - not how fast you get kills.
Don't make fun of me, but I think that it's freaking stupid that the game does not reward kills - just how fast you get them... That's really, dumb in my opinion...
Great idea for a tower defence game. Also good, since you added minecraft graphics. You should be more clearer on the dierections, though. I had no idea how to play or what to do when I started