This is an excellent book that suffers from what I call 100-Years-of-Solitude syndrome. It spans three generations of the same characters, and the allegories reiterate themselves from generation to generation. It's a good read, but any one of the generations would have been a fine book on its own, and in aggregate they don't do much more than hammer home the same blunt Biblical allusions. Is it neat that the three generations echo and rhyme? Absolutely! But it's a hard thing to keep up steam for over the long haul.
Anyway, that's the bad. The good is the book itself. There are lots of fascinating characters, each of whom exemplifies some aspect of human psychology. Reading through East of Eden feels a lot like casting acquaintances from your life into book form; there are lots of characters, and with the exception of Aron, each of them rings true. My girlfriend suggests that we can learn more about the human condition from fiction than we can from psychology, and books like these make me thing she might be onto something there.
Is this the best book I've ever read? No, but I'm happy I made it through. It could have used an aggressive editor, but the scale of the world, the characters, and the recurrent themes make it a breath of fresh air compared to most modern literature. I doubt this book will stick with me, but I can see why it's considered a classic.