Having now read all of Meyrink's novels that have been translated into English, I can honestly say that, although it is too bad his work isn't well known in English, it isn't surprising either. It is simply too challenging for most readers that don't have a specialized interest.
I will leave it to Mike Mitchell's excellent biography "Vivo" to recount the details of Meyrink's life. It is even well outlined in the introduction to the Dover edition of "The Golem" and needs no further recounting here. What is not so well known and is of interest is that Meyrink was an avid explorer of occult groups in the late 19th and early 20th centuries. He was, as well, a member of the Gold und Rosenkreuter order of 17th century, as well as the Asiatic Brethren, a Rosicrucian Order that specialized in Kabbalah as well as alchemy, and included many jewish members.
Working within such fraternities clearly Meyrink took up an active work with dreams. Throughout his works runs this one common thread, that the imagery is definitely of a world where dream bleeds into "reality" and real people can take up lodging in dreams.
In "Walpurgisnacht" Meyrink continues the thread of a world in decay, a world teetering on the brink of madness. Meyrink is even prophetic, writing in 1917, about the coming of the second world war. Here the world of dream doesn't seep into the world of reality, so much as it bursts through the walls and floods it in a flood of blood that sweeps all the characters along with it. In a sense, I think Meyrink is one of the 20th century's unacknowledged masters of Horror.
The eighteenth century saw two revolutions, the American and the French; and from these two revolutions arose two egregores whose titanic struggles paint the drama of the modern world. The child of the American Revolution is the thought-form of individual liberty, of a society of laws, and of "Law and Order" but not, as Ronald Reagan once observed, in a pejorative sense. The other child was insane from birth, and has given rise to fascism, to communism, to the killing fields of Cambodia and the planned starvation of the Ukraine. The goal of the one is the liberty of the individual, of the other the "heel of a boot in a human face... Forever", as Orwell observed. Meyrink clearly saw this titanic struggle and wrote about it in his last two works, and especially in this one. Obviously, he was pessimistic as to its outcome.
I highly recommend all of the works of Gustav Meyrink to those who are interested in the pioneering work of the exploration of the human unconscious, and for those who would like a glimpse of what the world might look like if the forces of that unconscious are simply let loose in the world.