This movie takes place two and a half years after the events chronicled in the original Aa Megamisama video series. As such, the relationships between the main characters (in particular Keiichi and Belldandy) have evolved offscreen to a certain point, and some characters that had been introduced in the manga only now make their first onscreen appearances.
However, that doesn't detract from this wonderful film, which, though very much a fantasy, is a story that is sweet, without being boring, and if a touch melodramatic, then not excessively corny.
Aa Megamisama the movie seemingly follows two tracks - examining the relationship between the mortal Keiichi and the seemingly submissive goddess Belldandy who has come to live with him - and examining Belldandy's own past, which is not as perfect as one would think. Especially when someone from that past starts a chain of events that could bring down all of Heaven.
It might take a while for this movie to be distributed on US shores, but it'll certainly be worth the wait.