I've just finished reading it and I thought it was O.K. I certainly see what most of you mean about it being overrated. There were no huge shocks.
One thing that disappointed me a little was that I found myself getting lost in Flynn's descriptions of virtually everything, some taking up almost two pages of not so vital information that veered away from the actual story. The ending, as a lot of you agree, was a let down and looked very rushed.
It's not bad, this is the second thriller novel I have read after Girl on the train and gone girl definitely comes second.