This is excellent in design, atmosphere, concept. I lost heart on level 4. I don't have the time to do a challenging lava jump and then hope I manage the bullet hell. Getting through bullet hell once to find the key wall was... well, yeah. Hard.
First time I went to level 2 went out of bonds and just kept falling into greyness. For a second I thought it was a joke game where you just keep falling and falling...