8. Your Cast Constrains Or Betrays Your Film's World
I'd like to, at this point, mention that for all the nonsense we've tolerated from him onscreen and off, Brett Ratner did a bang-up job with "Red Dragon". It FEELS like we're watching "The Silence of The Lambs" timeline a bit earlier, and he acheieved the same feel through performances, cast, and cinematography. It's one of the better prequels I've seen. But then, there's the small matter of Harvey Keitel. Keitel is good in "Red Dragon" as Jack Crawford, the FBI head who appeals to Edward Norton's character for help on a case. The problem is, amidst all this accurate rendering of the world we saw in "The Silence of The Lambs", Keitel is the betrayal. Jack Crawford was played by Scott Glenn, and his part in "Lambs" was substantial. Glenn didn't reprise the role because his research actually disturbed him deeply. It's a credit to the cast, crew, and Ratner that they succeeded despite this obvious difference. Nonetheless, it's impossible to not notice in the transition between films. And that's a prequel's first curse in regards to cast: Differences will betray your world, or jar you into thinking less of a story and more of the movie they're in.
Guilty Parties: It'd be remiss of me not to mention that throughout "The Hobbit", happy as I was to see the likes of Christopher Lee and Elijah Wood, they didn't NEED to be there. This is a rare case of the cast betraying the fact that they've been ADDED as a fan-pleasing exercise, and let's be frank - I'd love to know they were available to film further stories in the future, but they may not be. I understand that it's fun to have them there while they still can be and resemble their characters, but it drew attention to them when it shouldn't for anyone who's read the book and knew they were surplus to the story. (I'm guessing those who didn't read it just noticed the film was REALLY LONG.
Exception: ANY Prequel is also going to be scrutinized over the fact that you're often showing younger versions of established characters - And sometimes you KNEW what those characters/actors looked like and it doesn't match up. Stellan Skarsgaard had to be a young Max Von Sydow in the Exorcist prequel, and that's...not really what he looks like. (That said, his acting is one of the few good things on offer.) And I'll lift my ban on criticizing the Abrams' Star Trek to say that try as one might, it's IMPOSSIBLE to forget that Zachary Quinto isn't a young Leonard Nimoy. Nimoy being present doesn't help. (The rest of the cast could also be taken to task here, but they at least didn't have their elder version present onscreen with them. More on this later....)