Great concept, I enjoyed how the rhythm and combat game mechanics were tied together and the graphics remind me of He is Coming.
I wasn't sure why some of the gems were smaller or larger, made timing a bit more difficult, and when the bombs come it should say "press space" not "hold space", but an even better solution would be to either include a tutorial that explains bombs, or have [Space] somewhere on/near the first few bombs that appear.
One thing I would definitely change is the white flash each time you attack or parry a bomb, makes it harder to see the falling notes and in a rhythm game even a split second difference can be crucial for the timing.
Overall I enjoyed it and kept playing until I beat the boss, so I'd definitely recommend expanding on it.