The 1986 sci fi action film Highlander was an unexpected hit when it was released. It centres on a man who discovers he is immortal and must battle others of his kind in order to win a cosmic prize. It ends in a satisfying way with the hero triumphing over evil.
It was unnecessary for a sequel to be made. Despite this, Highlander 2 hit theatres in 1991. The story was seen as a betrayal of what made the original popular. It introduces aliens to the Highlander universe, a decision that added to the movies angry reception.
The key lesson to learn from Highlander 2 is to know when to end a story. Not every successful film needs to have a sequel made. This lesson is further emphasised by the fact that it is often called the worst sequel produced in the history of Hollywood.
Highlander 2 also shows us that the second movie in a franchise needs to continue the things that made the first one popular. If it veers into completely different territory then this can alienate potential fans. This can kill a film series before it has a chance to begin.