5-2 and 6-2 of DtP were always really difficult for me. They're not poorly designed or annoying, I'm just impatient and unskilled.
Ishras Ark in LV drives me mad, though. I rarely enjoy either trip. Other levels were a satisfying amount of challenge+charm, but the Ark levels were just tedious and dull imo.
There were probably a few handheld levels that bugged me but it's been so now long, I don't remember any. ┐(´－｀)┌