I really like what you did here! The mechanics are great and quite frantic. I managed to kill the first boss and struggled with the Swarm, as there is a lot of going on. I think the building part is really clever.
The the building parts die a little to fast and one has to constantly place some in between parts so the boss would focus on them and not destroy once wheel chain to in turn let the towers do their thing. I guess a little tweaking on their health part could help a lot, so one can really enjoy the building aspect of the game more :)
I really like the esthetics, sounds and feel to it! Job very well done.