Needs more work.
The player needs to know where the monsters come from. It's easy enough to put an arrow on the ground pointing into the map on the entrances where the monsters would come from and then perhaps a arrow pointing outward for the exit point.
Although you have a green marker indicating that you can place a tower somewhere, it still is difficult in finding where you can place them. The roads and town buildings make up the majority of the area and building towers are forbidden on them, so basically the player is fishing around the edges of the roads.
An enemy counter of some sort is required, as it isn't clear how many monsters you need to clear before you finish the stage. Stages can end in victory even though there were a few monsters still in play.
I never needed to use any of the last two towers-three of the third tier towers, plus some of the smaller tier ones along the right path of the final two stages if the money could be spared, are enough to clear the last three stages of the game. The fourth tier tower is not even remotely as powerful than placing three third tier towers in good locations, thus it's ridiculous to even consider buying it, and I haven't even touched the very expensive fifth tier tower.
The game actually has somewhat of a story, although it's a little weird how DEFENDING against attacks without any instance of engaging the enemy leaders suddenly leads to peace and prosperity after the sixth level. Did the evil guys just throw in the towel and disappear after getting thwarted six times?
At least you got a skeleton of a game out that is playable to a conclusion.