The scaling of the health values on the bosses are bananas, especially in comparison to how hard it is to create truly effective synergies. A reroll mechanic of some kind is necessary for a game requiring this level of efficiency, as is a more reliable way to remove unwanted pieces.
And the pool of pieces is insane! I love how much variety there is in potential builds and synergies, but unless you get crazy lucky you're never going to see anything come to fruition. You have to take huge swings in the early game (getting a zombie, hoping for a priest/paladin; get some scrap; hoping for a tinker; etc.) or win through no fault of your own (GET A HELL PORTAL ON TURN ONE!)
There needs to be a way to hedge against luck. Either by creating a "weight" system that makes certain pieces more likely to appear when other certain pieces are present, or have certain pieces only appear when other pieces exist (i.e. having Daar only show up and be automatically acquired when you have both a ferret, a bird, and a panther would be pretty neat).
I love the flavor and mechanics and style and effort behind this game, but it has some obscene balance flaws. Too many pieces feel like trap options, while too many others feel like "too little, too late" if you haven't been building specifically towards them.
I had a run with two sirens, two game devs, two thieves, a bunch of humans, and a tax accountant. I got really lucky in my ability to really make my humans do some real work on the field, but it still wasn't nearly as effective as getting a single item (hell portal) on the first boss. It wasn't even enough to get me more than halfway down final boss.
My experiences with the diversity demon were similarly frustrating. I worked to get one of each kind of unit, only to realize that I had only seen one single "structure" in the game that stuck around permanently, making the demon practically useless.
Oh, and some of the destruction mechanics just don't work. I saw books destroy themselves at least three or four times and only saw one bookshelf created as a result. I think it has something to do with there being more than three adjacent to each other creating an overlap in triggers or something.