From air by agatkha

every dr0me level is an underrated gem that people look at, think is a joke level, and then move on. I genuinely believe all of his levels are incredibly unique and I adore them for being so unique

don't know if this truly counts as underrated but pointzero by Ilrell, Digitalight and one of the greatest megacollab rosters ever came to mind.
I also like Enantiomorphs by LucasYecla99, which for a while was the rated level with the most objects (394K to be exact).

i don't think feral (66765209 )by inside get that much praise around the community, so imma suggest that

and ofc rgbwheregisgold (110928977) too lol

Rooftop Cigarettes by GaidenHertuny is one of my favorite levels of all time and has some of the best gameplay I've ever played alongside having some of the best level progression I've seen, I wanna go into more detail in my eventual review, but I think it should be more widely known

knot by santiachu

dunno just how much this counts but cool alien level by viot (86018967) is really cool

just check out everything by viot tbh

for a recent underrated banger the world of scarlet by excellent567

One of my favorite levels that so happen to be underrated is Double Electron by: Namtar. (ID: 10930245) PEAK PEAK PEAK PEAK PEAK PEAK