Hollywood has a miraculous ability to take a successful premise for a franchise and reusing it until it is well and truly dead, and then they continue to flog it. Sequels can establish franchises with an incredible sense of longevity, yet for each successful franchise there exists a multitude of failed franchises. The Hangover is a prime example of this; the first one was funny, original, and fresh. The second and third instalments of the franchise were little more than repeating the story in a new country, with few new situations. Other franchises simply do not lend themselves to a sequel; look no further than the cinematic abomination that was Jaws III. It is extremely hard to create a successful franchise; Star Trek was cancelled after three series, yet it has gone on to spawn one of the most succesful franchises in the history of cinema (both financially and critically). The longer a franchise exists, the greater the possibility for three key flaws to occur; repetitive plot lines, absurd storylines, or continuity discrepancies.
Honourable Mention - Shrek
When the first Shrek film was released it received critical acclaim and widespread applause. The franchise now contains four films featuring the primary cast, as well as a Puss in Boots spin off. Dreamworks recently confirmed a fifth Shrek film, well and truly justifying Shrek's place on this list. The first two were funny, smart and filled with hilarity; the final installments and the Puss in Boots feature film were almost painful to endure. They relied upon slapstick humour and failed to develop characters, causing the franchise to stagnate and become clearly little more than a money making endeavour. The series has been a financial success, but as we shall see making money is not related to making a positive franchise; everyone has walked out of a cinema with disappointment at some point in their lives, whether it is a book-to-film adaptation which has betrayed the source material, a poor comic adaptation or a simply unfunny comedy. Money does not take into account how audiences reacted to films, and this is an important point to note.