I love art and SF fantasy illustration and I am an admirer of Lovecraft's writing skill and imagination. The cover art on the book is great! The interior work does not suffer for quaility, so why the low review?
Because I found the book itself disappointing, it lacks inspiration. I have seen most of the images online. I don't doubt that many of the artist are fellow fans of Lovecraftian lore and imagery, but they (as far as I know) got paid to paint these illustrations for the CoC card game, hardly a paeon to the muses.
To be fair, I was warned by several of the reviewers of what the contents amounted to, it was the reviewers who were gushing about a book with a fair amount of mediocre art work that I could have paid less heed to.
If you are desperate for Cthulhu related images, get it. If your merely curious, let it pass.