I'm going to assume that if you're thinking of reading this, you've already read some of the Russell/Holmes books. In which case, let me say: 
 - it does atmosphere in a similarly professional way to the other books in the series 
 - the characters of Russell & Holmes are as joyous as ever, although Holmes barely appears until the second half of the book, and they do work best as a pair rather than alone in King's books. 
 - unlike some of the other reviewers I didn't find it much more unbelievable than the other books in the series 
 - unlike some of the other reviewers I didn't object to the lighter tone and outre comedic touches - I felt they fit with the silent movie seeing and feel. 
 So why have I only given it a three? 
 Almost nothing happens. It's a beautifully drawn, well-researched nothing, mostly peopled with characters rather than ciphers. But even so, there is enough plot for a story a tenth the length, stretched over 300 pages. It is filled out with meticulous descriptions of settings and behaviours which are fine in and of themselves, but smack more of a travelogue than a story without any plot to pin them down. 
 This is one in the series I won't be rereading.