Flowers of Evil took the interesting approach of having different characters from the series sing the opening theme at different points in the series. Here are two of them.
Nakamura's theme is abrasive, pitchy, and laden with profanity; Saeki's theme is lyrical, sweet, and very Japanese. Yet despite the harsh contrast, at the end they're singing the same melody.Flowers of Evil - OP (Nakamura)Flowers of Evil - OP (Saeki)
The ending theme is ... unpleasant. Yet as it lurches along, a strange rhythm emerges, that wraps its tendrils around my throat and doesn't let go. Had I studied music, perhaps I could express why I believe this is somehow technically superb, even though it sounds awful.Flowers of Evil - A Last Flower
Disclaimer: Even if I may think all of these are good
, Saeki's theme is the only one I actually like