Pretty solid game! However I'd love it for there to be more progression feeling for the player by having levels, or perhaps the towers can passively level up, or you can upgrade them with different pathways and upgrades so you have different builds, kind of like Bloons TD. Maybe the player can have a variety of different skills to bring every fight too. Though I have to agree partially with TheGamer where the UI feels a bit slow to appear which makes the prepping time feels not enough at first. To increase engagement maybe the player can also have unlockable skills, maybe different weapons too.
I think a good game reference for this should be Castle Defenders II, which is a tower defense game where the player can also fight alongside the towers!