I’m glad you had the same thoughts about this story as I did. Honestly, I was a bit disappointed reading this, having the other M.R. James stories I read in mind. It’s anti-climactic and not working in the use of character focuses. I also think the story was too short to introduce and form the side characters well, who are now a bit out of the blue.
You asked what readers thought was good about the story, but I don’t know, other than the already mentioned pretty humoristic chattering of the Anstruthers and the writing style of M.R. James.
As a writer one of the few traps I never fall into is the leaving out of real consequences of the characters’ actions. (It’s one of the errors that really stands out when rereading your story, so I don’t think James reread this story very well.) Putting the scary or thrilling parts at the right moments and in the right focus is something else: I often find it difficult when to hint instead of put something in full light (or vice versa) or not to wait too long to give the reader a well-deserved thrill (the reverse of what James does here). I think that’s the craft lesson for me here: paying more attention at timing and focus of the thrilling/scary parts.