Undercooked
This was almost a great game. Nice music, good graphics, and an interesting concept. However, after that the game starts to fall apart. The smaller fonts are really tough to read. The fact that popup menus don't go away unless I click "no" or an equivalent is maddening and in a game such as this it results in the screen becoming littered with unwanted balloons. The upgrades are far more expensive than a new tower and their advantages aren't that powerful, eliminating a lot of the incentive to spend money on anything but new towers. Once I figured out the upgrade system, I found myself wishing I could just drag the element onto a tower to add it, but instead I have to open that tower's menu, select the element I purchased, and drag it into the available slot. It's just too much hassle for a fast-paced TD game.
If you make another such game, I just hope you'll spend a little more time on it. This game has a lot of potential, but it's really unfriendly to the user and that kind of ruined it.