Fun, but not enough variety
This game has potential--it just needs some variety.
First, there is really only one enemy type. Despite different skins, they all appear to take the same damage from all tower types and travel at the same speed. There is no motivation to have a varied path or a variety of towers or to place key towers such that they can catch air units. Second, too many of the towers are outright useless--the saw is head and shoulders better than the other basic-tier towers. The missile launcher is not cost effective compared to the bomb tower. The laser tower is a waste of money compared to a single well-placed poison tower. The only upgrades that are actually worth it are tier 2 bomb tower and tier 2 poison tower. Worse, just one charge coil is basically game over, and two or three charge coils is more than is necessary to kill every wave of creeps in the game. The towers and upgrades really need to be balanced. Finally, the towers all just do damage and no interesting side effects, like slow or stun or reduce armor or otherwise.
6/10, 3/5. It's fun, but a little too vanilla for a genre as played-out as the Tower Defense.