This is an enjoyable watch. The fantasy elements don't feel completely contrived, and the characters are above average on the believability scale. The main character is never the whiny little baby that some people will portray him as (though he does have some issues), and he does grow and change as a person throughout the show. To those who found Kadowaki's hatred unbearable, I can only say this: I found it very true to life. Hatred seldom follows a logic others would understand (a concept that Jigoku Shoujo explores both thoroughly and believably). Someone may hate you for thesmallest of slights, for being kind to them, or even for no reason at all. Once this person has decided to hate you it can be very difficult to avoid making things worse. If you ignore this person, he may hate you more and more. If you attempt to reconcile, your efforts may only feed his spite.

some other notes:
I'm still wondering why the switching thing was necessary. Effectively the same story could have been written with only the fantasy side, and the story doesn't do much with the Japan side.
This isn't exactly the best soundtrack to come from Outani Kou...