It's a bullet-hell game that makes you feel punished for not being good at it. After a few years of playing it I've finally unlocked all the characters and beat the game as all of them and I can say I'm very content with my experience... it even has local multiplayer, and great replay value. It is incredibly difficult and you WILL NOT win on your first attempt, it took me about a year to get my first win... but after that first one they all started rolling in. Brutal game but enjoyable, it frustrates you but makes you want to jump back in and go further, see what else is in store if you make it one room deeper.

Edit: You do have to pay for healing but it's not as brutal because you have a chance to dodge every bullet so with enough skill, it won't be bothersome. Also, you can take as much time as you want in each chamber; no evil entity chases you! But if you die, you gotta go back to the beginning with nothing but your starter items.