Fun game, with an interesting concept. A few noted bugs.
1. Prices for turrets are incorrect (lvl 1 auto turret says 50, but costs 150, tho i did notice the price of each turret base increases each time you place one, which i did like).
2. Health is not being tracked properly. (Arrow pointed at 150 tho the number said 350).
3. Not really a bug, but add either new waves, harder enemies after awhile, something! once you get three turrets on each of the four edges of the center you can walk away and rack up the points.
Again i like the concept, keep it rolling with some updates.