I have tried the game. It is not very stable.
First, the game suddenly drops down FPS when spawning new bunch of enemies.
Second, sometimes you have no more spawn, because you killed all of the enemies, but the game didn't noticed that.
Third, I couldn't buy second upgrade and I don't know why. I could select research centre, but I couldn't buy anything.
So my score for this game is quite low, but if you repair those bugs, the game will be playable.
Also the idea for the game is OK. I like this type of games.