What a cool game !
Sometimes sponge have 0% but still a type of resource (maybe liked to obelisk).
We don't know the cost for turrets. And we need (for the future) visual feedback to know how it's work (turret attacking, damage taken, base and sponge range of absorption and flow).
It's hard to tell where are our sponges. Maye some feedback on the mini-map.
Sometimes I just want to take a sponge but I build a turret, because it's the same trigger and structure can collapse.
I don't use the rotation of turrets (except for the first wave). Maybe it could be cool to build turrets anywhere ? And maybe move them like sponges ? If you want to go further in your move / drag and drop gameplay.
I hope there will be turrets upgrades and new kinds of monsters too (maybe some with long range shot and you have to move your turret to them).
Movement camera on the map is not so easy. Maybe if you allow arrow to move the camera a little it could be nice.
Anyway, good job, I enjoy it :)