I'm reading Mark Z Danielewski's House of Leaves now. Being a rather massive book with copious footnotes, I saw a comparison with Susanna Clarke's Jonathan Strange & Mr Norrell. While that book is longer, this one probably takes a lot of people longer to read. The reason is that while JS&MN is a fairly straightforward narrative, and the notes basically do their own thing, Leaves is all gnarled up. There's a section in the first half where the type runs backwards and forwards (lot of printing tricks here) and it gets hard to tell text from footnotes from footnotes to footnotes.
How is the tale itself? It's kind of a trip. I might have enjoyed Clarke's book more, but this one has its rewards, certainly. Johnny Truant is an interesting creation in that his LA wastrel life brings him smack against the uncanny. In the main he's a Chuck Pahlaniuk character—which essentially means a Bret Easton Ellis character with more intelligence and less money—but sometimes he turns into a raving genius out of Lovecraft.
There are a couple of genuinely disquieting scenes, like Holloway's freakout in the labyrinth and the Pekinese story. MZD isn't an author I see myself emulating, but I'm sure there are pluses to doing so.