Really cool tower defense game !
The character and enemy sprites look awesome, it's just too bad they are not animated :( but regardless real cool designs here.
Gameplay wise i like that this has mouse aiming, and the upgrades menu has quite a few choices available.
My main gripe is that these waves seem to be a bit too overwhelming compared to what you can affoard after surviving the first wave, that's really a LOT of enemies from the start :o but nothing a bit of balance tweak can't fix.
Other than that it's a strong base, it's already fun to play, and thanks to the sprite designs the game has a lot of character to it.
Well done :)