One of those sequels that, rather than progress the storyline or characters of the original, chooses to effectively press the reset button: the Ghostbusters have disbanded so we must watch them reform, and Bill Murray and Sigourney Weaver have split up so we must watch their courtship again. The film's lighter, more kid-friendly tone is at least off-set by spectacular visual effects and an imposing villain.
I don't get all the hate. For a sequel this movie is still impressive, but I think the first one was definitely the better film. Much can be blamed on the general family friendliness compared to the original.