Liked the game. One thing I'd improve is to add some indication on boss room doors. Often they're right at the spawn area, or I just not readdy to deal with boss yet, but I can incidently encounter him anyway.
Biding of Isaak has indication of boss and other special rooms, it only adds an another layer of stretegic thinking: am I strong enough to fight boss at the moment? should I risk spending resouces to get upgrades? how exactly should I spend my resources?... also it minimizes the ammount of mindles wandering on the map.
Your game is quiet different from the Binding of Isaac though... IDK, it just feels a bit unfare when I was dying from bosses for the said reason.