For me, terrible sequels have one consistent aspect, regardless of the franchise. Invalidating the first movie. There seems to be a tendency for filmmakers to want to put everything back to how it was at the start of the first movie, which leads to some incredibly lazy writing. Look at Ghostbusters II (Oh, no one believes in ghosts despite a giant stay puft marshmallow), The Force Awakens (Han's a smuggler again and Leia a rebel), Men in Black II (we're going to undo Tommy Lee Jones' character's happy ending), Jurassic Park/World sequels (John Hammond changed his mind like 3 times on whether a dinosaur park is a good idea, and he had all these secret business partners we never heard of). A good sequel develops themes and character arcs without pressing a reset button.