I rather liked the Black Rose arc; Mikage was one of my favorite characters. It seemed as though it was written more to showcase a philosophy and the peripheral characters than to develop the main characters, which is cool. After watching the show through some-odd-times the Black Rose Saga seems rather integral to establishing the theme; it is the first time somebody 'leaves' the academy by becoming aware of the illusory nature of the place, and it is revealed that students in the academy do not age / leave their adolescent mindsets so long as they are there.

Regardless, the Ohtori Akio and Apocalypse Arcs still ruled over all.

And, hell, I thought the characters were meticulously realistic and beautifully-written. They were my imaginary best friends back in the day. They still have a special place in my heart.