If you only buy one volume of H P Lovecraft, don't buy this, buy Necronomicon by the same publishers. But if you want to buy more than one volume, make this the second. This is stuff "left out" of the Necronomicon, and while some is good, as a whole its not as good as the contents of that book. Ever bought a "Best of, Vol 2" album? Well, this is a little like that. A few hits, and some "not hits".
The stories are in published order - and includes some early stuff not professionally "published" at all. You can see the beginnings of Lovecraft's style in this early (1916 onwards) work, but it is clearly not his best stuff. There is a fair chunk of poetry here too- probably 50 pages out of 400-odd of fiction- and as a rule there are a lot of very short stories, with some almost fragments of ideas. It is definitely interesting to compare this to Lovecraft's later work, and the later stories get better as you would expect.
There is also an interesting essay on writing horror by Lovecraft himself as well as the history of publishing Lovecraft in England by Steven Jones. All up this adds another 100 plus pages to 430 or so of prose and poetry. The inside covers have the distinctive Virgil Finlay commemorative sketch of HPL in shades of blue, which is a really nice touch.
I finished up my review of the Necromonicon by saying I wasn't going to purchase more Lovecraft; but this Black Book changed my mind. I'm not really sorry about that, but this is a companion piece to a greater work, not a starting point for an introduction to HPL's works. If you are a HPL fan, grab a copy, and treat the review as 5 stars; if you are a more casual reader of HPL, don't shed too many tears if you miss it.