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.
In Amplitude: M-80 and I Am Hated, for their incredibly fast strings of repeated notes, and Rockit (2.002 Remix) and Out The Box for their incredibly complex patterns, depending on which portion of the game you're better at.