Very good overall
Very good game so far I hope though that you'll go further with it.
Graphics are good, although maybe something to adjust quality, espcially for the later levels and when you have towers.
Style of the game is good
Sound, the Level 10 has great sound, although I didnt enjoy the rest of it
Violence, not too much a violent game in my mind, shooting made up creatures
Interactivity was great, complete control only failing due to the speed of my computer and changing levels
Humor, it wasnt meant to be funny really
*Please speed up the first level, at a point it's boring.
*Please offer more upgrades for gun power especialy after the level curve as you put it.
*please please please make it longer, if you can just add more enemies each time and make it progressively harder with more upgrades availible
*Keep working on more