I can't quite tell if the Holmes stories are serious literature or something to mindlessly consume. Some of the stories are quite serious and weighty, but an awful lot of them seem too neat and twee to take up much space in my head.
The Case-Book of Sherlock Holmes appears to have been written long after Conan Doyle was thoroughly sick of writing about everyone's favorite irregular. The stories are all okay, none are really objectionable (except for the painful racism in "The Adventure of the Three Gables") but none of them really shine either.
It may be that I make the mistake of reading huge gluts of Holmes at one time - swallowing up ten stories at a sitting and re-reading the books frequently enough that they always stay fresh (and therefore predictable) in my mind.
One way or another I'm done with Sherlock and Watson for the moment and I'm quite happy to leave them alone in their foggy London, so full of muck and mystery, until the shine has worn off and I can read them as fresh and exciting again.