okay

The game is alright but it needs more stuff. I think it's too linear. It would be more fun if there was more upgrades and special abilities. It could also have a bit bigger playing area that you could explore. And the enemies appearing out of thin air was weird. The turrets should instead be stationary and moving enemies should move on to the game screen.
Instead of "50 challenging levels" you should have like 10 bigger and better quality levels because I don't think many will play this for 50 levels. It's a bit too repetitive.
If you make a third edition, consider what I said. It could be a good game but right now it's lacking.

Fun but odd

A fun game, but haveing enemies just appear randomly all around you seems odd.

Turrets should appear stationary off screen to the right so that you come up to them. Mobile enamies should appear off screen in any derection and move onscreen.

nice

the slow movement of the tank cannon suprisingly makes this game harder, very well done, music suits.