Interesting game! I enjoyed the mechanics and the turn based nature of the game. I went for a similar "less health = more hp" route with my game. I'm usually not a big fan of turn based games, but this one was really fun for me. I enjoyed the old school graphics and the simple sound design.
If you wanted to improve, I suggest modifying the random generation of the maps. Level 2 was super long for me, level 3 and 4 then both had me walk into one room off the spawn then into one other room to leave without fighting any enemies. The game also crashed when I reached the shop screen. I also took some cheap hits in doorways when I didn't realize an enemy was coming through, some sort of indicator one is coming or just not having them spawn like that if the room they're coming from is unexplored could help a lot. Those changes plus some music would make a phenomenal game.
Check out my game if you get a chance!