American culture is obsessed with originality, innovation and novelty. Or at least it thinks it is. Wired Magazine reported recently on a study done by Nicholas Christenfeld and Jonathan Leavitt of UC San Diego that finds that spoilers actually increase the enjoyment of written stories. Stories need suspense, obviously, but it seems that too much suspense detracts from the experience of the story. A little foreknowledge allows us to focus more on the story and less on our reaction to it.
I have long felt that originality is not the most important factor in whether something is any good. Consider the epic poetry and tragedy of the Greeks; such literary heavyweights as Homer and Sophocles were telling stories everyone already knew by heart. Or think of any story about history, or biography. What is important here isn't the what but the how. Originality is one factor among many.
In most cases where people criticize something as being unoriginal, predictable, a rip off, or whatever, what they are really saying is that it was unsatisfying. This may or may not be traceable to lack of originality. Art needs stability. Like rhythm in music or meter in poetry, there is an ongoing dialectic of unity and variety. Stability is boring, but there needs to be enough to carry the variety. Variety is chaos, but there has to be enough to give us a charge and keep us on the edge of the seat. We can't totally have either one, but we can't totally give up the need for either. That is the magic of dialectic.
There is also a personal agenda behind any critical discussion. Cynicism should not be mistaken for intelligence; bemoaning how derivative and unoriginal everything is is a great way to display superiority to everything. Enjoyment involves naivete.