Superb game, definite frontpage material.
But it could be improved:
On the levels screen you still use "u" in the place of "you", changing that would make it look a lot more professional.
There isn't much of a path for the enemies to follow, they just cross the screen, therefore eliminating the possiblity of strategic tower placement.
Keep up the good work.
This is great. I love all this alien thing. Plus it is a good defense game with wonderful graphics and design. Well done.