I can tell all the core things are in, now it's just making the rest of it that supports the core gameplay... the enemies and bullets ignore walls. clearing a room spawned a white cube in a middle section that was out of reach. The shop window can't be closed. If I could offer one bit though... there should be more impact for when enemies are spawning in to show where they are coming in at, when they hit and are hit, and when defeated. Generally you either want dangerous enemies that are difficult for each one to be defeated, like a boss rush, or a bunch of small enemies that are only dangerous as a group... right now it's kind of neither, with them coming in one at a time. A good example might be the praire king minigame in stardew valley... each enemy is easy to kill, but the challenge is in how many spawn.
The last thing I want to point out, is I like the idea of the shooting being musical notes... but it needs work. right now it just plays a random note everytime it's fired, which sounds nice... as long as you don't spam the fire, which given the type of game you would want to... and very quickly shows the limited number of notes it plays. Something you could look into, is have a soundtrack of some kind "playing" in the background, and then each time it fires it simply "turns on" one note in that song. That being said, if not that, a stricter limit on how fast you can fire would help at least keep it from being as noticeable.