Heh, reading this thread is like reading a list of some of my favourites. I loved Wuthering Heights, really liked Catcher in the Rye, loved War and Peace. The first 400 or so (lol) pages of War and Peace was a bit of a slog to get into so I can understand how people might give up, especially on the random essay parts (just skip them if you don't like them, they're not necessary), but after that and I got used to it I breezed through the last 800 or so.
I say it's all a matter of perspective. You may say "couldn't get through"; I say "partway through until I get back to it".
Now those I have a few of... But I'm pretty optimistic and I hate leaving things unfinished for good, so it's a rare book that I'll completely give up on.
I can't think of any right now that I've completely given up on. I did put Ulysses down years ago, but I was determined to eventually come back to it, and now it's on my challenge list for this year, so wish me luck...