Almost awesome. But the weapon pickups make no sense. There seemed to be three colors of letter, but they all did the exact same thing. Try a different paradigum, like "normal weapon, and then letter pickups make your weapon cooler for 5 seconds" or something. The zoom out for boss fights was brilliant though.
Besides the turn rate being really annoying, your tutorial makes you pick the apache, shows you how to shoot, and then points out how stupid you are for bringing the apache on a rescue mission. Nice.
On the aquarium, the bottom right pavement tile is clearly different, but doesn't count as a difference. How can you have a difference game that can't copypaste?
Really cool, except for the not healing bit. If something can be accomplished by sitting around being bored (hide in a corner to regen) then you should make it free. Basic game design. Don't hate the player.
Love the art style, but with every level being the exact same and no skip-forward button, this is the worst of the worst kind of TD. 2/5 for the art style though.
Get rid of that extra layer of menu to upgrade a turret. 99.99% of the time you want to upgrade when you select a turret, .01% you would want to switch the type.