By the time you can afford to generously spread rocket launchers you practically own the game, and at some point the wave generator only spawns Mega Tanks...
I tink the game could use some sort of win condition...
One little bug I found is when the list of enemies in the forecast is long enough one has to scroll down, if you're at the end of the list and start the level, the scrollbar flips between its current position and the top of the list where the number of incoming enemies gets updated.
I love the amount of different turrets and enemy types there are. All very well done and the wave forecast is nice to have.
The turret range circles are a good feature, too. The circle of the turret to be placed could be emphasized so it's easier to make out among the others. Maybe give it some neon(-ish) glow that fades when the turret has been placed?