I finished up the Book of Tyrael tonight. I don't know if it was quite as nice a lore supplement as the Book of Cain, but taken together, I now feel like I know everything I need to know, indeed everything there is to know, about the lore and canon of Diablo. It's mildly interesting. The books have some cool art, at the very least.
Reading these Diablo books and my recent purchase of the Dark Souls Design Works art/development book, I feel like I should pick up something similar for the Assassin's Creed series. I know there is some sort of Encyclopedia of the franchise, though it may only go up through ACIII.
Anyway, that's another book burned for '14. Next up is the inspiration for the STALKER game series, Roadside Picnic.