Let me just start off by saying that Ah! My Goddess! is my favorite anime and favorite manga to date. It has kept this rank since the first time I watched an episode back in 2006.
There are so many things I love about this series. I love the artwork, I the dialogue, the romance, the general story line, and, most of all, I LOVE the characters.
It's quite ironic, as the story is meant to focus on Kiechi and Belldandy, yet my favorite characters are Urd and Hild. I will find myself reading the manga or watching my favorite episodes just for a glimpse of these hilarious characters.
Urd is Belldandy's older half sister, and is half Goddess and half Demon. I don't want to give too much away, but lets just say that this is a constant source of interest in the series, and always causes problems. I always find that the Urd centric parts of the series are the best as well. ;P
Hild is Urd's mother and (Spoiler alert!) the ruler of demons. She's like... A more insane version of Urd. Whenever she's around, trouble is sure to follow, as well as hilarity.
The main characters (Belldandy and Keichi) are good too, I just don't find them nearly as good as their demonic counterparts.
They also have the most irritating romance of any book, movie, manga or anime I've ever seen. It's so frustrating, that my friends and I have found ourselves yelling at the screen or throwing our manga across the room. Seriously. It's great though, because it really keeps you reading/watching, hoping to finally,
finally, see them break out of their "kindergarten level romance" and into something more.
The other main supporting characters are Skuld, Urd and Belldandy's kid sister, Megumi, Kiechi's younger sister and Mara, a demon who is constantly trying to get to the goddesses, and is also used as comic relief.
What I love about this series, is that the supporting characters really make the story. Great main characters are good, I mean, just look at the success of Twilight! (take that how you will), but when a main hero/heroin can go to their sister/brother/friend and that character can truly make a contribution to the story, that's what I want to see.
The way the novel progresses isn't like in a book where the entire series is leading up to one cataclysmic event. Instead there are a lot of little, "major" events that make up the story.
There are two seasons of Ah! My Goddess and I still hold out hope that a third will be made. It's just that good.
Seriously guys, go watch this!