The challenge is just in that sweet spot where you can do it after losing a couple of lifes (or continues in places like level 8), but you end up hating so much those damn green ghosts.
Everything is really really polished, so great game! 5 stars in every aspect.
Some little bug I discovered on my first run: if you create a hole at the side of a level (just by the end), fall in it and move to the side (going to the other side of the level) you get stuck without being able to do anything. Everything else was absolutely perfect!