One of the best stories in this collection, the title story, "Skull-Face", is also one of the worst. The best bits are the atmosphere of decay lying at the heart of imperial London; the cosmopolitan and diverse nature of the society shown; the main character's presentation as a person ravaged by the trauma of fighting in the trenches of WWI; and, as might be expected with Howard, an unrelenting forward momentum through the plot. The worst bits are, essentially, the same as the best bits: The decay of empire, which is taken without question to be a bad thing, is blamed upon the diversity in society; the response to trauma is set as a personal failing requiring redemption, rather than as an injury unjustifiably inflicted; the pace of the plot allows no time for reflection upon the issues raised, indeed the issues are not recognised as such, as the story is a conservative exercise in the need to maintain the social and political status quo, and which is therefore not questioned. Beyond the inevitable imperialist tenor of what is a variety of the "Yellow Peril" pulp fiction trope, Howard brings in more overt racist and white supremacist elements than I recall from Sax Rohmer's Fu Manchu stories (which I've not read for some time), though perhaps that transparency is a good thing: the racism is not cloaked at all.
I found the worst story in the collection (and in my recent reading) to be "Black Canaan", set in the US deep South, it is a white supremacist wet dream which I couldn't finish.
The other stories in the collection fit the common apologism for pulp fiction works of this era: that they simply reflect the commonly held views of the time and place in which they were written. Accordingly, these other stories have racism as incidental or secondary features of the narrative, rather than being the central theme. It is possible for me to read around the racism in those stories to appreciate the weird horror elements that I'm actually interested in, but they are still a distraction.
Re-reading this book after several decades of life experience is an interesting and instructive exercise, and one which leads me to a reevaluation of Howard as a writer, and as a promoter of conservative libertarian, and white supremacist, ideas. That I've downgraded my rating by only one star is due to a nostalgic sentimentality for the undoubted escapist pleasure Howard's stories gave me as a youth, despite their ideological underpinnings.