Jean Baptiste Monge has posted a a couple dozen sketches he created for the Book of Cain on his blog. The sketches are all very detailed and expertly drawn, ranging from Tristram to the Hellforge. There are a LOT, and I’d recommend checking them out.
The post has some commentary on the things that Jean Baptiste liked about some of the sketches. Some of the interesting comments are that he “enjoys the babies in the jars” frame and Charsi‘s tattoo.