Very cute and nice idea for tower defense by sandcastle-building. I really wish the walls worked differently, but not sure how, maybe just slowing enemies but without taking damage? That would allow general rebalancing. Currently I find towers to be way more useful if not OP with use of Attack Buff Towers.
It would be gerat to have more visibility which towers are actually affected by buffs.
I also wish the castle building, as much as it's lovely visually, also had mechanical effect.