High School of the Dead is godawful and easily the worst animé I've ever seen. Admittedly, I do pick my animés with care so I haven't seen that many horrible ones, with HSotD, Noir and Tokko being the worst I've had the misfortune of seeing.
Watching the first episode of HSotD, I thought it seemed promising. A little bit too fan-servicey, but aside from that, there was nothing blatantly wrong with it. And it's got zombies, so I thought, if it at least turns out to have a halfway decent cast, it might be enjoyable. But it had to have one of the worst casts ever. I seriously can't remember the name of a single one of the female characters.