Has the foundation of a good tower defense game. First thing I would do is making the terrain naturally more restricted, and players should only be able to build towers off the enemy's path. The walls could stay but enemies should be able to destroy them. You could even take cheese bits from your health pool and place them as "walls" they attack first. To make it cost something and avoid spamming. You should keep going! There are jams specially to finish ongoing projects, if you want another event for feedback