The worst movie sequels ever made from throughout film history. These are the follow-up films in a franchise or reboots that brought the most disgrace to a once-beloved properly, and most completely abandoned the elements that had made the first film popular. In many cases, these terrible sequels even abandoned core concepts, characters, and ideas that had made the initial films successful - as when the Joel Schumacher Batman series ditched Tim Burton's dark, gloomy sensibility for candy-colored cartoon theatrics, or the "Jaws" series left realism behind and became a flat-out shark horror series.
Follow-up films have always been a huge temptation for movies executives and studios. Name recognition and positive sentiment towards the first movie means a better chance that a sequel will fare better at the box office than a random, unknown title. Additionally, contracts are often signed before an initial movie is made locking in talent for a second, and even third, entry in a potential franchise, meaning there is less up-front dealmaking and casting to be done before production can begin.
In the case of franchises that are essentially 'locked in place' prior to the release of the first movie, like the "Harry Potter" and "Hunger Games" series, these pre-negotiations can be even more all-encompassing. Often, sequel films are shot simultaneously with the original film, or immediately after production has ceased on Part 1. Richard Donner and producer Ilya Salkind famously attempted to shoot "Superman 1" and "Superman 2" at the same time before the idea was abandoned. The concept was again taken up by Peter Jackson when he made the entire "Lord of the Rings" trilogy of films at once.