Quick, who was the first writer to have short fiction published in Playboy? Okay, admit it. The only reason you answered "Charles Beaumont" is that you saw who edited The Fiend in You. Beaumont was a brilliant writer who died far too young and under sad and terrible conditions, but he left behind a body of work that anybody would be proud of.
This anthology, as you can see from the Table of Contents, has stories by big name writers and some who aren't quite so well-known. Many of them are stories published within a year or so of the anthology publication, but there are some older ones as well. Richard Matheson, one of several Beaumont friends whose stories are here, gets to open and close the anthology.
Well, sort of. There's something after Matheson's second story that's not mentioned in the ToC. It's a short, uncredited essay titled "The Reason for Ballantine's Chamber of Horrors." It's a rationale for reading horror stories. Was the original title of The Fiend in You" supposed to be "Chamber of Horrors"? I haven't a clue.
Another little curiosity is that Stanley Ellin's story is listed in the "Acknowledgments" as having originally appeared in Stanley Ellin's Mystery Magazine. As far as I know, there was never a magazine by that name. Maybe Ellery Queen's Mystery Magazine is correct, but that's just a guess.
All that aside, this is a dandy little collection that as far as I know has never been reprinted. If the story titles intrigue you, inexpensive copies are easy to find on the 'Net.