We spent a lot of time conflicted about the difficulty. Too easy and, yeah, you can just spam your way through. Too hard and it just gets frustrating. There are several axes of design that we could configure, e.g. number of enemies, number of projectiles, enemy HP, your *own* HP, hit box sizes, etc.
In the end we settled on a normal difficulty to start, and adding a "challenge run" button after you beat the game.
Thanks for the feedback!