They took away the Maitlands (you know, the ghosts in the attic), turned Betelguise the great manipulator and ultimate perverted evil of the Neitherworld (he was buried for a reason, you know) into Beetlejuice, an antiheroic jokesterm, and created a world outside of the Maitlands' home for Lydia (now a somewhat happier, but still goth girl) and Beetlejuice.
They basically stripped Betelguise, Lydia, and the Deetzes (they didn't acknowledge that Mrs. Deetz is Lydia's stepmother) from a barely PG-rated film (color me crazy, but how did that film, which dropped TWO f-bombs [one scene in which Betelguise grabbed his crotch], end up with a family-friendly PG or at least a teen-friendly PG-13 [and I know PG-13 was around when the film was released]?), added wacky neighbors and characters, and created a kid-friendly series. It's magic.