This is the collection Neil Gaiman's famous, Hugo-award winning Sherlock Holmes/Lovecraft Pastiche/Alternative History fanfic "A Study in Emerald" was published in.
This is a bit of a problem.
Neil Gaiman is one of these bold writers who can make even fanfiction into something special. Putting him in front of an collection of similar stories written by people that are not him... makes for a startling drop in quality. Especially when his story is followed by one where the author clearly just replaced one character's name with Irene Adler's and hoped nobody would notice.
So, yes, the collection is a mixed bag. It is situated thematically in the curiously large intersection between non-canon Sherlock Holmes and Cthulhu Mythos. Both areas have had a large amount of fan-written and professionally published stories, with a dash of crossover between those two that goes back to at least the 1980s. And it mostly works quite well: there are some genuinely creepy Lovecraftian stories in there, and there are some that catch the spirit of the Sherlock Holmes stories, and some stories actually manage both. Some even mix in some other characters and elements for good measure, H. G. Wells features as a Watson substitute in one story for example.
Others are not so great. Some are clearly fix-fics for Sherlock, some clash with canon (both Sherlockian and Lovecraftian), and at least one has a blatant Mary Sue touted as Holmes' "ideal woman". And they all would have been better if the authors had tried to have some internal consistency at least. Having a dozen stories in a row in which Watson encounters the Necronomicon for the first time does not help.
All in all not bad, no complete stinkers, and with some real pearls in between.