Underworld by Don DeLillo. He is one of my favourite writers, yet I thought his most well-known and critically acclaimed novel was a load of crap. There is one extremely long scene where he spends 50+ pages describing a baseball game, which I can safely say is one of the most tedious reading experiences I have ever had. After a few hundred pages of feeling nothing whatsoever, I decided to stop wasting my time and put it down. To paraphrase something someone said about James Joyce (that I didn't agree with, incidentally) it could have done with a good editor.
If the book said one interesting thing about America, it said too many American writers are obsessed with filling as many pages as they can and attempting to write something that one unimaginative critic will inevitably call 'the great American novel'.