2. The Absence Of Tension And Unpredictability
In prequels, anything you recognise from the original film will survive relatively intact in order to keep a sense of continuity. Which takes away a lot of tension and unpredictability because you know right from the start that any returning characters won't be on the list of the dead at the end of the film or experience some kind of huge change in their lives like suffering from a permanent disability. In X-Men: First Class for example, we know that, whatever happens, Professor X, Magneto, Beast, and Mystique will all survive unharmed because we've seen them in the first three films. As far as X-Men prequels go (Apart from Days Of Future Past because of time travel and alternate timelines being plot points), those four characters are effectively immortal. Whatever struggles they face, they will always make it out alive. Which robs the film of a fair bit of its tension. It's the same with The Hobbit trilogy. Because Lord Of The Rings was made before The Hobbit and we've already seen an older Bilbo Baggins, we know that he will survive his adventures with the Dwarves Of Erebor in perfect health. Which makes any scenes where Bilbo is put in mortal danger less exciting because we know that he'll either find some way of getting out of there alive, or that the other characters will back him up and manage to save his life. Or (and sorry to keep coming back to them) the Star Wars Prequels. Obi-Wan Kenobi, Anakin Skywalker, Chancellor Palpatine, Yoda, R2-D2, C-3PO, Boba Fett, Bail Organa, Chewbacca, and Mon Mothma had to survive the Prequels because they all play a part in the Original Trilogy. We also knew that Padmé Amidala was going to die because Luke and Leia's biological mother being dead was a core part of their backstories. And although it looks great, the climactic Lightsaber duel between Obi-Wan and Anakin in Revenge Of The Sith is free of all tension because we knew the end result years before the film came out. Obi-Wan was always going to win the duel and leave Anakin crippled, causing him to be put into the Darth Vader suit in order to fit in with A New Hope. By virtue of their links to their source material, prequels will usually have a considerable lack of unpredictability that makes it harder for them to genuinely surprise the audience. Which does tend to make them less enjoyable since we can work out what's going to happen.