A Challenge!
I'm sure you've heard this over 200 times now, this game is freakin' hard!
The concept of this defence game is flawless. The only thing that could be considered 'bad' is the difficulty. Although I can't keep myself from continuously trying to beat this game, others might not be so hardy. I don't say this often, but I think lowering the difficulty a little bit might improve your ratings in the future.
Also, there are a few glitches. Occasionally at the beginning of the game, the 'base' you have to build has the red outline wherever you move it, and if you click the outline dissappears completely and there's nothing you can do except look at the pretty orange planet. Also, sometimes the prices of buildings also glitch. Sometimes the fist base upgrade starts at $700, and I figured out a way to purchase hospitals for $250 no matter how many you have.
In summary, AWESOME