I think the start is good, where you make the player draw a path, so the player knows the main mechanic. However, the second level throws too much things at you at the same time. Took a while before I understood where the carriages were spawning. You have upgrades (I think? blue?), range (and damage? green) and you can also directly draw paths from spawn to the towers (is worse than getting the bow/green first?). Giving everything green arrows seems as the optimal strategy, but got overwhelmed fairly quickly. Some enemies stay out of range. My advice would be to introduce each element one at the time, and make the player notice what changes each time.