I'm with Arch on this, if you've read whatever series/book(s) a show or movie is based on you automatically compare it to what you imagined when you read it, unlike someone who hasn't read anything and instead gets to witness the awesome with virtually no preconceived vision of it.

And by far the biggest downside must be to already know everything thats going to happen during the entire show's lifespan... that would completely suck >_>

Thank fuck i never read the books indeed.