If you’re a fan of the whole universe these series of movies are creating than you may like the last key as it acts like a flagship for them.
Its very trivial, more about the fandom and the geekiness, but the big problem is is that it lost it scariness in the process.
So the first movie had Elise and her crew of ghostbusters as the supporting characters to the bigger picture, then in the next pic the sub characters become the main ones as we go through the orgin of how they met each other. The last key continues from that point, and because of that it changes the demographics of the film. Still a horror movie and still a ghost story, but the focus on the lives of these ghost hunters does not make the film frightening enough any more.