I really enjoyed both Harry Potter and The Life of Pi, but I did read them whilst I was much younger. It gives me great pleasure to return to the books I have read as a child and get a second reading from them. I don't think I've really ever been let down by a book, apart from one without a proper ending where 'it was left to my own imagination' which thoroughly irritated the eleven year old version of me. But I suppose it was never really over-hyped.
My opinion on Twilight, not that anyone really cares, is that it is very readerly, however not at all writerly. There is no style as such, unless you count overuse of adverbs, however the situations and plot is aspirationally sympathetic to the current generation. By which I mean Twilight fulfils a certain desire of its desired market. Stephanie Meyer might have written absolute drivel, but the fact remains that she is a very financially successful and well-known author.
Actually, I have thought of one over-rated book, Bill Bryson's the Lost Continent. It was a bit of an effort to read. Oh well. I would be interested in hearing what anyone thinks on this matter.