Anything by Charles Dickens. Don't get me wrong, the meat of the stories themselves is amazing, but the writing, ugh. He wrote serials for periodicals, he was paid by the word, and OMG is shows. His plots are great, but the writing is wordy and tedious. Take the opening of A Tale of Two Cities. The famous quote that begins It was the best of times, it was the worst of times... That single sentence goes on for over 100 words. Tedious. Boggy. Mind-numbing. Seriously, rent a movie or go see the play.
Tolstoy is difficult, if better written. It's the names. There's just so many of them. Each person will have one name and a couple nicknames, then there's names for horses, dogs, even swords. And the sentences don't usually have those clues that let you know what the names are referring to. So, you can find yourself thinking which chap is this now? and eventually figure out it's this other dude's sword. Worth reading, but keep a list so you know which name goes to what.