[Andrew H.]

It does seem strange to make a list of the most difficult books rather than the most difficult *novels*. Philosophy books can be hard to read because the ideas are complicated - but as far as that goes, you might as well include any number of advanced calculus or physics books.

Faulkner is hard to read because of the style it's written in. (The same is true for people who have trouble with Dickens - the language is modern but the style is not). The "Faerie Queen" is hard to read because the language is archaic and because it's poetry. Shakespeare can be hard to read because of the difficulty reading Early Modern English, but changes in language aside it's not that complicated. Here's an example of the original Shakespeare followed by Shakespeare translated into the current vernacular:

CAPTAIN
     Doubtful it stood,
As two spent swimmers that do cling together
And choke their art. The merciless Macdonwald—
Worthy to be a rebel, for to that
The multiplying villanies of nature
Do swarm upon him—from the Western Isles
Of kerns and gallowglasses is supplied,
And fortune, on his damnèd quarrel smiling,
Showed like a rebel’s whore. But all’s too weak,
For brave Macbeth—well he deserves that name—
Disdaining fortune, with his brandished steel,
Which smoked with bloody execution,
Like valor’s minion carved out his passage
Till he faced the slave;
Which ne'er shook hands, nor bade farewell to him,
Till he unseamed him from the nave to th' chops,
And fixed his head upon our battlements.

CAPTAIN
For a while you couldn’t tell who would win. The armies were like two exhausted swimmers clinging to each other and struggling in the water, unable to move. The villainous rebel Macdonwald was supported by foot soldiers and horsemen from Ireland and the Hebrides, and Lady Luck was with him, smiling cruelly at his enemies as if she were his whore. But Luck and Macdonwald together weren’t strong enough. Brave Macbeth, laughing at Luck, chopped his way through to Macdonwald, who didn’t even have time to say good-bye or shake hands before Macbeth split him open from his navel to his jawbone and stuck his head on our castle walls.

So I don't think it really makes sense to compile a list of "difficult" books comprised of books that are difficult because of subject matter, books that are difficult because the language has changed, and books that are difficult because of their complex style.