A good game though seriously imbalanced
I had fun with it for about 15-20 minutes; then I bought over kill and the laser cannon. After that it's pointless to play. You can't lose. When I finished, my base had 14,000 hp, I had 7,000, and I had 60,000 exp to spare. I would say remove the jackhammer and focus on making weapons scaled so that there's still incentive to play after 20 minutes or so. Add more levels of guns instead of a few levels then a HUGE step up that will guarantee your success.
Otherwise a great game, survival mode is a blast and captures the essence of what I think you were trying to go for in this game.