I thought the hound was appalling. Why not just use the power of suggestion instead, as they did so effectively earlier in the episode? Early in the hound sequence I did think they were going to reveal it to be an image/film being projected, which would have at least partially excused the jerkiness and overall shoddiness of the hound, but no. 
Also, I didn't like the constant going on about Sherlock's shortcomings/Aspergers'/whatever, particularly John saying explicitly that he has Aspergers'; I prefer it when they show him doing or saying something 'not quite right' and leave the rest to the viewer to surmise.
Was cringing at both the sub-Matrix arm-waving during the mind palace sequence, and the phrase 'mind palace' itself. I thought this was also another example of things being spelled out too much ? why did John have to explain Sherlock's memory technique to the scientist? It's much better when we just see a few visual snatches of what's going on in Sherlock's mind as he makes his deductions, but the details of the process should IMO remain opaque ? we are after all meant to be inferior to him and his amazing mind.
Russell Tovey was rubbish as Henry. Unconvincing and one-note.
On the upside 
, I thought the direction was brilliant ? cinema-quality, and I loved that it seemed to refer visually to films/TV shows from various genres ? proper old-fashioned horror, sci-fi, modern X-Files type suspense. The atmosphere was good and foggy/mysterious Liked Sherlock trying too hard to make it up to John after they argued, and equally liked that he was doing it at least partly in order to be able to do the experiment on John ? nice and heartless . Although I guessed almost as soon as John walked into the lab that it was a set-up by Sherlock.