Good game
It's a good game, my only suggestion is that you cap the level of the drones... as I'm writing this, the game is playing in the background... I haven't clicked on a single thing since about 1.2 million points, and it's now at about 4 million and rising. There must also be a bug somewhere as well, because somewhere along the line I lost one of the long-range drones and a short range (I think? It's the grey one). They just dissapeared... I've scoured the screen looking for them and they're nowhere to be found, and I can't buy new ones either.
Anyway, a cap at around level 50 for the drones would be a good idea, with them all at 50 I still at least had to shoot things myself. Right now in my game (that's still running, ~4.8 million points right now), all the drones are level 75 and just having the three red (Assault) and three black (Defense?) drones spread out a bit near the front of the screen keeps everything dead automatically. I think my game's only set on medium (it was the first time I played it) so that might have something to do with it as well, maybe Hard would be different, but that's my 2cents anyway. This is also my first review, hazzaa.