We do have plans to introduce a boss health bar at some point and my current plans for the Krystal conundrum is to add a regen system where under 5 will slowly refill your ammo but you'll be better off on your first go or two without using it so as to learn the patterns. After all, classic megaman doesn't really reward you for using your ammo and still dying to a boss. It's sort of more meant for knowing when best to use them like in a speed run mode but I feel like it's very much intentional that you can go through the game mainly using the fire and the weapons are bonus. Little secret though ahh... there's no damage differences yet until we get more weapons which is coming soon(tm). Of course, that's not what we got in at the time yet so yah know.
But thanks for enjoying it!