Its a great book with more information than someone can retain no matter how many times they read it. I found that taking notes as you read helps. But that makes it more like a text book than a leisure read., Albeit it Excellent material. Someone who says they knocked out a couple chapters in one sitting in my opinion did not take everything they could have from what they read.
Dude, I was barely even able to finish half a chapter in one sitting....
I did manage to finish The Silmarillion the first time I began to read it in earnest, but I can sympathize. It isn't structured like a novel; it's more like both a history book and a religious text. It's probably best to take one's time with it, taking breaks between the different stories.
I still consider it part of my canon even though later writings changed it. For some reason, I'm particularly miffed about Orodreth's and Gil-galad's parentage getting changed. I stick with the published Silmarillion for my canon; I don't want to change it.
I pretty much devoured it. If there was one book that influenced me in my youth, it was the Silmarillion.
RIP to all the brain cells that died trying to read the Lay of Beren and Luthien... To think that was the abridged version too...