The animation is highly stylized without being snobbish.
The still images are as attention getting as they are "dangerous/mysterious," adding sharp contrasts to the silly dancing the characters engage in.
Perfectly sets up the visual relationships of teacher and students, while also preparing the audience for the schizophrenia of the show.
I'm not a big fan of the OP song (Hito Toshite Jiku ga Bureteiru) on its own two feet, but it works admirably well with the theme of the opening animation.
Can't think of anything
Synopsis: Any opener which has inspired as many farces as this one has should go down in the books as a good opening animation. Combining high levels of style and symbolism (though the purpose of said symbolism is questionable,) it engages the eye and doesn't let go of the viewer. Yet, when the sequence ends, you both prepared and unready for what is to come next.
Popular farces on the opening: