Interesting that so many chose Moby Dick. It is a very unique work of art, to be sure. There's a block of about 200 pages in the middle of the book that is essentially a whaling textbook. This is extremely difficult to get through. However I think the book is brilliant and Melville's prose is still superior to any other English language writer I have read. His sentences, his vocabulary, are quite simply stunning. I can't count how many sentences I read in that book and realized that it would probably take me 20 minutes just to form a sentence this perfectly and lyrically. While reading that book, I was literally consumed by a feeling of disbelief that a single human being could sit down and create this from his mind. Genius. So don't look at the book as boring or exciting. It's a false and childish dichotomy. Look at conquering this book as an intellectual achievement, like working out your brain. Reading and understanding that book is something to be proud of IMO.
As for boring books, off the top of my head.....
I love Camus, The Plague and The Stranger are two of my favorite books of all-time, but I thought The Fall was oddly boring. I may have rushed through it and perhaps a second read would change my mind.
Recently read All The Pretty Horses by Cormac McCarthy and I thought it was far weaker than all the other books of his I've read. Probably 3/4 of that book was fairly unexciting.
Huge Kerouac fan, but I thought Big Sur was kind of boring, at least relative to On the Road and Dharma Bums.

