I loved this book. I agree that the plot is a bit messy, complicated, and at times slightly ridiculous and hard to believe. But not any more so than many other classics in the genre.
It does have about 100 or so pages that moves fairly slow, however there really isn't a good place to put it down for the last 250 pages.
Don't give up on this one.... you'll be happy you stuck it out till the end.