What a wonderful idea, with a charming presentation. Was really inspired by all of the upgrades and the many different ways they interact with the gameplay - there seems to be a LOT of design potential in this game! I think this could totally be expanded into a larger game if your team was interested. There's a lot of roguelikes out nowadays that feel relatively derivative of each other - but this one truly felt like something special to me, with a totally novel approach I'd never seen before.
When it comes to the bosses, I'm torn between wanting a brief intro screen of what their special ability, or being okay with just embracing the roguelike nature of the game and having the player have to discover their ability. It was frustrating losing to the Slime because I totally mis-evaluated how long I had to deal with it... but it also felt VERY roguelike, you know?