It's magnificent. Fast at times, brooding at others. I learned. I laughed. I got a bit emotional, too. It's really just about everything you'd want from a novel — no wonder it's a freakin' classic (says Captain Obvious).
Beyond the obvious (the creative re-tellings of the Cain and Abel story; the Hebrew word Timshel — which is Adam's last word, and which means "thou mayest": the core idea of the novel, that we can choose to reject bad and be good, or we can choose not to; and the wonderful descriptions of the Salinas Valley, Steinbeck's beloved home), there are two things I'll remember most about his book:
1) Steinbeck's quotability. Over the course of reading this book, I tweeted a good half-a-dozen passages from the book, and marked about two dozen more. Here are a few of my favorites:
"A story has in it neither gain nor loss. But a lie is a device for profit or escape. I suppose if that definition is strictly held to, then a writer of stories is a liar — if he is financially fortunate."
"No story has power, nor will it last, unless we feel it is true and true of us." -- Lee, one of my favorite characters (see below).
"Humans are caught — in their lives, in their thoughts, in their hungers and ambitions, in their avarice and cruelty, and in their kindness and generosity too — in a net of good and evil. I think this is the only story we have and that it occurs on all levels of feeling and intelligence. Virtue and vice were warp and woof of our first consciousness, and they will be the fabric of our last, and this despite any changes we may impose on field and river and mountain, on economy and manners." (This seems to me about as clear a statement of Steinbeck's personal philosophy as you could gain from this novel.)
2) The characters Samuel Hamilton and the Chinese servant Lee — two of the wisest, noblest, most dignified characters in any literature I've ever read. The two recognize each other as kindred spirits early in the novel — and become fast friends. Throughout the novel, they guide the other characters, helping them to choose good instead of bad. Samuel and Lee both guide Adam out of his malaise after Cathy shoots him (Samuel punching him around is one of the great scenes in the novel), and it's Lee who constantly guides Caleb through his moral dilemmas and attempts to be good, because, as Lee says, "The greatest terror a child can have is that he is not loved, and rejection is the hell he fears." Indeed.