Bad
I'm only giving you points because I liked the idea of the game, but everything else is just bad.
This game is so freakishly unbalanced. The difficulty curves are just... Never before seen on Newgrounds. I'm impressed and upset at the same time.
On easy, the waves take so long to spawn I could start the game, get some defence up, leave my computer on and go to sleep, wake up and go to school, get home and do my homework, watch TV for an hour and come back to see I'd only be on wave 25. You said there was a "next wave" button but I never saw one.
On medium, I started and got wiped out pretty quickly and realized what I should focus on to start the game, so I adjusted my strategy and got owned again. I kept trying and trying but even when I spent ALL my money on power stations and defence, I could never kill all of the ships because there would be too many for all of my lazors to kill because I couldn't afford enough power for them to keep shooting.
I haven't even bothered the hardest difficulty, I'd imagine it would be next to impossible since, aparently, the waves have more strength, health and spawn faster AND you have less money to start. Anyone who can beat that without cheating deserves a fucking medal of honor.
As for the features...
The little one liners the alien keeps pulling out of its ass get annoying after about... the 2nd message. There should be an option to turn those off.
The music was sub-par at best. It does capture that outer space feeling but it gets hard to listen to after a while. Thanks for having a music toggle at least.
This game really needs some kind of a grid on it so we can see where we're putting our stuff so they line up and there is no wasted space.
We should have a full view of the planet so we can place some extra buildings on the outer rim of the planet. Every time I try to drag the planet over, which I have to do WHILE I am about to lay a building, the game puts the building where I clicked to drag the screen over. That gets a little troublesome after a while.
I suggest you test your games before you actually release them. Good luck with your future work.