Charlie Anders over at io9 has a fun post about why prequels are evil. 

To make her case she says, in part: "But prequels aren't just boring and predictable - they're also morally wrong and a scourge on humanity, because they portray people as helpless pawns of a history that's already set in stone. Click through for five reasons why prequels are actually evil." She then talks through some specific problems and relates them back to the Star Wars prequels and the J.J. Abrams Star Trek prequel (though I'm guessing this will actually end up being an alternate universe story). 

The five reasons she elaborates on are:

• Prequels are anti-creativity
• Prequels are anti-futurist
• Prequels are anti-heroic
• Prequels are all about trivia
• Prequels are small and personal

While prequels can be all of those things, I don't think - by definition - they always are. There's not enough space on this blog to describe the things wrong with the Star Wars prequels. But one of the things that is right with them is their essential prequelness - that is finding out how Anakin became Darth. Yes, doing a prequel does constrain some things you can do plot-wise but that does not mean they are by definition anti-creative.

And there are lots of examples in genre fiction where prequels have worked well. I was particularly impressed as an impressionable teenage spec fic reader with Isaac Asimov's second Foundation trilogy. In those three prequels Asimov manages the quite substantial task of unifying his foundation novels with his robots and empire novels. This required a lot of creativity but he pulled it off quite well in my mind. They were also big stories that were at the same time small and personal - connecting two of Asimov's most memorable characters. People will criticise the books but I suspect those criticisms are probably ones you'd level at much of Asimov's writing.

But there are other examples too - The Silmarillion, the new Dune books and others. Again, just because some future plot aspects of the stories these books are telling is constrained it doesn't mean they can't tell a good story. 

Novels face all sorts of constraints. It's these constraints that drive good authors to tell better stories.