Score: 497657
Dood...
There aren't very many points of contention for me. I like all of the turret attack animations for a successful hit, the random enemy that deals 400 Gold, the various types of waves (The color coded touch was nice), the ability to advance to the next wave... There were a lot of good things about your game!
A few pointers:
When clicking between a lower level turret and a fully upgraded one displayed incorrect stats for the turret.
When clicking between 2 turrets of the same type that are fully upgraded, it shows stats as if it hadn't been fully upgraded, yet you cannot upgrade it. (In game, it isn't an issue because the turrets seem to be doing the max level damage anyway)
The area of attack seems smaller than the radius shown. (Try making the turrets start to fire before they enter the radius and connect exactly when they cross the radial attack area)
The attack area for the turrets on the left, bottom, and right sides cross over into useless void.
Being able to sell or move Towers should be available for a price or for free, as the case may be.
I guess more Turrets couldn't hurt.
Being able to replenish HP for Gold should be added.
A pause function should be added... I needed to pee so badly during this game.
A restart, new game, and/or renew enemy waves button(s) should be added.
The same enemy coming over and over again didn't really bother me all that bad, but other people might get bored of seeing the same thing. Add some more enemies.
While attacking enemies with the Water Tower, I noticed that they sometimes return to normal speed, as if there is a glitch or something.
This is just a suggestion... What about being able to combine two different, max level towers to form a new tower that has both functions of it parent towers, but starts at level one and can be upgraded from there?
Other than those things that I mentioned, it is quite an outstanding game.
I give you major props.