Would love to see this expanded more! Maybe more enemy patterns and the ability to choose which tower to place? I really liked how sometimes one giant boss would come at you instead of a lot of small ones. I didn't know what the differences between the towers were but the variation in particles was fun!
The graphics are great! There's a lot of enemy variation, did you model all the kaiju yourself? The only gripe I have with the graphics is that the Japanese text didn't make sense. (the billboard on the right is also upside-down)