Mediocrity is a curse
This is not a bad game.
That does not mean it is a good game either. For a tower defense game it offer too little in the realm of interest. The basis of the game? Hold down the mouse and shoot little walking enemies until you get enough money to buy things. Upgrade your base to continue clicking and killing... wash, rinse, repeat. The mission mode is boring and most of them just involve buying a certain base equip. and then using it against the enemy.
If you want to kill your mouse, your eyes, and your hands... play this game. If you want something challenging? Well this will definitely challenge you to see how masochistic you can be.
Play this game for a few minutes. Enjoy the visual effects of the tiny soldiers going pop when hit with an artillery shell from an assault tower... marvel at how their tiny weapons can damage a base... and then move on. It's not worth spending much time on this game.