I think there's two things that make me love this series. First of all, while vampire stories have been done so many times, as have romantic comedies, Karin is one of the few cases where the author tried to put a new spin on both genres, and actually succeeded in doing so. Second is the characters. Particularly Kenta. Usually the leading female role of these series falls for a whiney, brooding little brat. Karin's love interest goes completely against this archetype, with an upbeat attitude and a great work ethic (sort of like a male Tohru Honda, but tougher). Karin herself does have some of the usual traits of the lead female of a romance series (clumsy, no experience with boys, a victim of fate), but she manages to differentiate herself from the others. Many other characters are not so original, but still manage to be entertaining. It's a great series to read and watch, especially if you don't typically like romantic comedies.