Aerial Garden bothers me for two reasons. I do really like the vibes, and I really enjoy the tight platforming, but these issues really kill the Zone for me.
1.) The bees. If they were finite, then, sure, but they are not, from what I can tell.
2.) The kill-plane being so close the platforms is unfun. On one hand, I understand if the idea is to let the player die quickly, so that they respawn quickly. But, there are some characters that have the mobility to save themselves if they fall just short of a platform, but it feels like the height of the kill-plane was made with Sonic specifically in mind, perhaps. And speaking of;
Egg Rock Zone. An issue I do have with SRB2's official levels is that many can have instances of heavily layering instakill hazards about, and, I really, greatly dislike this. Namely, crushing hazards and bottomless pits. I feel they should hurt you like a regular damage-type, instead of instantly killing you. But, because they do not, Egg Rock and Arid Canyon Zone are examples of stages I have grown to dislike because of how unfun playing on them can feel. It has the feeling of playing in a bounce house (/pos), but touching the walls electrocutes you and unplugs all of your computer's cables without consent.