Having successfully evaded Middlemarch in college (I thought it was too hard), I am now reading it (via audiobook, with the Modern Library edition at hand) completely enraptured. It reminds me of another reason why children's book professionals need to read books for grownups:
Buyers of the Middlemarch newspapers found themselves in an anomalous position: during the agitation on the Catholic question many had given up the Pioneer--which had a motto from Charles James Fox and was in the van of progress--because it had taken Peel's side about the Papists, and had thus blotted its Liberalism with a toleration of Jesuitry and Baal; but they were ill-satisfied with the Trumpet, which--since its blasts against Rome, and in the general flaccidity of the public mind (nobody knowing who would support whom)--had become feeble in its blowing.
That's not only a long sentence, with a confluence of colon, semicolon and em-dash that even the Horn Book wouldn't let you get away with, it--I'm guessing--entails some aspects of English history about which I know nothing and care less. But I'm a confident enough reader to make peace with my ignorance and keep going, even while I remain defeated by Eliot's epigraphs: "Qui veut délasser hors de propos, lasse--Pascal."
Young readers are put in this position all the time, meeting words, sentence structures, and extra-textual references for the first time. It's salutary for those of us concerned with their reading to put ourselves in their shoes, a circumstance more likely to occur for us in reading books for adults. Hard books, the definition of which being completely self-determined. When we hit a patch of French in a novel, we--at least those of us not educated to the standard Eliot expected of her readers--can look it up or shine it on, but either way we're challenged by a text that doesn't give itself up easily. That choice comes more easily to the veteran reader than to the neophyte who's still underlining each word with a finger. Learning how to skip is just as important to reading as learning how to persevere.
But reading difficult books is not just a reminder of how hard it is to learn to read. The sentences in Middemarch are often enormous but also enormously dense--Eliot uses an awful lot of words but few seem extraneous. You really have to pay attention, especially with the audiobook--let your mind stray for a few seconds and you're lost. But the reward of such required concentration is absorption, a rare and welcome state in a clamoring world.