We tried to explore 2 faces of what could be a ball rolling bullet hell, all the rooms before the boss are as much as careful planning as dexterity, some even letting you choose to complete the level in a peaceful way without even killing an enemy without consequences since we also decided to take the scoring out, going for a much more peaceful experience.
The boss on the other hand is pure dexterity and patience and we wanted it to feel like hitting a wall after all the peacefulness and really mean the end of an adventure.