As a part of my research into developing Lovecraft: The RPG, I have been researching both the original stories by H P Lovecraft and also some of the academic research available. I just finished H.P. Lovecraft: The Decline of the West by S T Joshi. Here is a brief review for your interest.
This book looks at both H P Lovecraft’s letters and also his stories and analyzes Lovecraft’s evolution of thought over the years – ethics, aesthetics, politics and metaphysics. Lovecraft had no problem expressing his opinions in his letters and, depending on what stories he was working on at the time there are interesting parallels.
It looks like ST Joshi took the title of this book, and the original essay he wrote that became this book, from the same title of a philosophy book by Oswald Spengler. There is a good reason for that since Lovecraft was much enamored of Spengler’s work.
ST Joshi attempts to trace many of Lovecraft’s philosophical ideals to other sources, either by content or by direct reference from the letters. This is very illuminating in understanding Lovecraft’s notion of weird stories. I have read ST Joshi’s excellent biography of Lovecraft and H.P. Lovecraft: The Decline of the West proved very helpful in refining my understanding of his approach to fear of the unknown as it relates to the common man.
H.P. Lovecraft: The Decline of the West is an academic work, more so than the biography, but its very worthwhile reading if you want to have a greater understanding of Lovecraft’s works.