I just rewatched and found little to disagree with on this thread.  There are wonderful bits and pieces and potential for something truly classic but it falls somewhere in the middle range.  It just feels like a muddle in terms of story, with too many bland good-guy characters on the periphery.  Maybe if one strong heroic character had emerged to oppose Rathbone, it would have helped crystallize things. 

Interesting observation in Universal Horrors by, I think, an editor who worked on the film, that all scenes rise to a dramatic pitch, leaving little variety and a lack of pacing.

One comment complained about the dollhouse motif, but I wonder how much more confusing the film would have been without that device.  The dollhouse is the only thing that provides a kind of "through line" for the film.

Also interesting to me that, despite his obvious bloodthirstiness, Rathbone's relatively restrained here, actually playing less "villainous" than some of his scenes as the generally well-meaning Wolf in SON OF FRANKENSTEIN.

Also, wondering what it was about Karloff that made him such an effective physically intimidating figure on film.  He is truly imposing as Mord.  He wasn't the biggest guy on the lot.  But there's just something about him:  that glower, those eyes.  When he faces down any other character, there's no question who's going to win that argument.