It's funny to me that the whole "Salinger is overrated" thread revolves around Catcher in the Rye, with no mention of his other works.
There's a good argument to be made that Catcher in the Rye is, indeed, over-rated. (It's one of those books which is so highly regarded, and so widely read, that it can fairly be called "over-rated" even if you think it's pretty good). I would definitely argue that "Nine Stories" is a better piece of work. If you haven't read "The Laughing Man", you should take half an hour out of your life and do it immediately-- I think it's one of the best short stories ever written.
(Short digression: I once had the pleasure of meeting a successful writer of musicals, and for some reason, I spent 20 minutes talking to him about how I thought "The Laughing Man" would be great to adapt into a musical. The writer seemed to be amused by the whole idea, or at least he didn't try to back away from me slowly. Of course I now realize that the whole conversation was moot-- he never would have gotten the rights!)
"Catcher in the Rye" belongs to a very specific genre which, let's face it, not everyone likes. It's a coming-of-age novel about a relatively wealthy and privileged teenager who is being groomed for a specific type of wealthy and privileged adulthood, and who realizes at the start of the novel that he does not want the sort of life he is being groomed for. (See also: Siddharta, Tonio Kroger, and on and on).
Not everyone wants to read a novel about that, and that's fine. But I think Catcher in the Rye will keep attracting fans simply because the narrative voice is so distinctive. Remember when the Onion published an obituary of Salinger that was written in the style of Holden Caulfield? Everyone got the joke, because Holden's voice (or even an imitation of Holden's voice) is one that you recognize immediately.
I'd also argue that what Salinger did-- writing a full length novel which is narrated by a child/adolescent-- is pretty hard to pull off successfully. Mark Twain did it with Huckleberry Finn, and there was a good novel by Mark Haddon which did the same thing (The Curious Case of the Dog in the Night-time), but I can't think of too many other examples.