1. The volumes that they have read are mostly visual volumes, consisting of art books, art instruction volumes and comics. There are few novels in their lists.
2. The ratings given are mostly 4 or 5 stars, with very few 3 stars. I guess they fear to offend when it comes to giving their true opinion. It is also possible that they are so heavily invested in the books that they have read that they give them high ratings, but it is unlikely for one of the artist given how many books he has on his list.
3. Comics form a significant amount of the volumes read.
4. Non-fiction volumes, except those for art instruction, seem to be close to non-existent. They either do not read them or they have not listed them. The former seems likely, they are likely to be extremely focused individuals.