Quite a lovely game, played until floor 11. The main gameplay loop is pleasing as fuck, music and sound effects are good and the graphical style is neat.
For long term engagement I think this would work well with some kind of outside system, while satisfying I think you need something more for players to get really hooked. Perhaps some kind of outside progression system outside of combat, such as investing in a village or something like that.
Also, more varied areas, more songs, necromancer character, bard character and a monster character.