These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Catharsis Factor - Dream 6 is this, with your ability to destroy the girders that plagued you in Dream 5. The two dreams even have similar endings, with the girders emerging from the surroundings trying to stop you, but where Dream 5 forced you to dodge around them or get shocked, in Dream 6 you just blow through them unimpeded.
Nightmare Fuel - Apparently, people have said that they were scared after getting shocked by electrified structures in Dream 5. Understandable, given that until this point the game seemed not to even contain any form of damage-taking.
Dream 5 in general, really. The storm makes everything grey and hard to see, the music is melancholy and just a little off-key (and the flowers you collect are very off-key), and your actions do nothing to actually make things better or brighter. You just blow through, with little consequence, and the Dream doesn't have an ending scene at all, it just fades out when you get near the finish. The dream's flower looks droopy and sad even when fully restored
Crowning Moment Of Awesome - Gather all the petals in a level, fly high up in the air and discover that you are now the petal equivalent of a Chinese Dragon. 15 minutes later, you'll still be chasing your own tail.
That One Trophy - Pure, which requires you to not only get through the entirety of level 5 without getting shocked even once, but collect a host of purple flowers inbetween some very tight spaces, where touching anything will get you sizzled. Turns the zen atmosphere into one of controller-pelting fury.