Great game, highly addictive! Would recommend.
Bugs I found:
Paladin doesn't kill vampires. And neither does priest. He doesn't count them as undead either.
When you use "half health next boss" item, it disables the box jellyfish passive and it doesn't count it as damage done to the boss. It doesn't count anything after as damage done to the boss.
Doctor doesn't do the "less than 3 health, medikit returns all health" thing that it should.
If you have a monkey or engineer, then you can't continue after saving. Edit: You can continue after saving, but you mustn't save on the first turn when the boss shows up. So, save only after the first turn. It does autodeploy but doesn't let you attack. It happens even if you don't have monkey or engineer.
Ideas for the improvement:
Arc of the covenant shouldn't destroy priests and paladins and change them to ghosts.
Succubus is too steep, should be if you have more than 6 health, not 4.
There should be more ways to remove things from militia.
I'd wish that you get a freebie choice, rare and two uncommons after killing every boss. I know it is set up that you get your choice after boss attacks.
I wish that dire wolves and death worm have global reach.