Mark O'Connell contemplates them:
You finish the last page of a book like Gravity’s Rainbow and—even if you’ve spent much of it in a state of bewilderment or frustration or irritation—you think to yourself, “that was monumental.” But it strikes me that this sense of monumentality, this gratified speechlessness that we tend to feel at such moments of closure and valediction, has at least as much to do with our own sense of achievement in having read the thing as it does with a sense of the author’s achievement in having written it. When you read the kind of novel that promises to increase the strength of your upper-body as much as the height of your brow—a Ulysses or a Brothers Karamazov or a Gravity’s Rainbow—there’s an awe about the scale of the work which, rightly, informs your response to it but which, more problematically, is often difficult to separate from an awe at the fact of your own surmounting of it.
The Dish 