Thanks for playing and for the feedback! 😄 The “hold D” thing is actually something I've been thinking about. Reaching the end is intentionally quite accessible, but most of the challenge is in getting all three stars, collecting the coins and reaching the harder upper routes. Doing that forces you to fight the momentum quite a bit instead of just going with the flow.
That said, I think you make a good point about giving the basic route a little more challenge too, so I'll keep that in mind! And I'm glad you liked the boss fights — I wanted them to break up the flow and give each world a proper finale. :)