Mandatory reading for any student of the horror genre. I recommend it for both its historical value as a horror piece and its glimpse into Victorian society from a point of view quite different than the usual 'proper' literature.
Unfortunately for me, I found "The Great God Pan," to be so inhibited in its approach and so formal in its language as to be nearly inaccessible to me. Granted, it was written in Victorian England and, at the time, the sensuality and un-Christianness of the book scandalized London, so I forgive much and made a concerted effort to read between the lines. In the end, I found the visions of horror Machen imagined interesting, but his depiction of those visions, and his characters, too cold and sterile for my 20th Century taste.