An absolute blast, almost everything I'm looking for in a roguelike. I've beaten the game about 4 or 5 times now and it doesn't get old. A wide variety of strategies to play with the wide variety of weapons, multiple upgrades to carry you through the journey, and a tough, unique boss to top it off! I have almost 0 problems with this game.
With that said,
problems: The knockback upgrade seems useless as enemies aren't... you know... knocked back, and the bullet bat is next to awful.