Great game.
I really enjoy the art style for this game, it's simple and fits the game, without being too complex. My only peeve with this is that you used an 8-bit arrangement of Chop Suey, by System of a Down, for the opening and credits, and didn't credit that, and it really should be credited as it is (okay, I guess that's a bit insignificant, but that's just me, I'm like that lol). But other than that, great job. Your game is highly addicting, a great characteristic for a game like this to have. I like the part where the alien has his little moment, and you play on the cliche, it's great comic relief. And you've got a nice little twist on a decades old concept, and, despite it being and old and not that original, it's still a unique touch to this kind of game (the upgrade and story system, I am referring to). I award you a 4/5, 9/10. Good luck with future projects, and have fun with it.