another latecomer...
I think it's safe to say that TEH wouldn't be first choice if you had to pick an episode - no matter who chose, fan or casual viewer.
I got the feeling, that here on the forum many very active fans didn't like episode 1 as much as the others. Or at least there was more potential for critical response... I joined here only after series 2, but I think the focus was so much on the Reichenbach episode that critical response for series 2 fell short. Now that we don't have something similar like the fall, maybe people take more time to consider the episodes in detail. Also the expectations were incredibly high and hard to meet.
To me, the fan service in TEH felt like a slightly desperate attempt to meet expectations and not to disappoint. Maybe with tongue in cheek, but still. Problem I had with this: I want to keep the fine line between what's in my head (shipping and stuff) and what appears in the show. When I say I would like to see this and that, then only half of it is what I actually need to see - the other half is fantasy that, if I am very honest, I would prefer to stay only fantasy.
That's why I didn't like the Molly/Sherlock and Moriarty/Sherlock scene until it was revealed that it's only in Mollys/ Mrs. Hudsons imagination... which I thought was cleverly done, and made it perfectly okay for me because it was there with a background. friend of mine without any fandom-contact said: "ohhh, that's the housekeeper imagining they have a relationship? the one who also said they only need one bedroom?" ...she understood that part perfectly well, although she doesn't know anything about shipping. same with molly, same with the "fan club"... the media attention in TRF hints at a fanbase, there must be more kitty rileys, and any viewer who has seen the first two series won't have a problem understanding series 3, imo. I don't know about casual viewers, but I have to agree - to jump into a series somewhere in the middle and to expect everything will be easily understood... hmmm, no. if they like it, or even only parts of it, they can easily provide background with watching the other episodes.
Personally, I fell in love with series 1 and 2 without any effort... for series 3, it took patience and lots of re-watching until I could fully appreciate it and with TEH I never quite succeded. I got the impression others went on the same journey.
Friends of mine, who patiently waited for series 3, but haven't been much (or not at all) involved in fandom, had similar feelings for TEH.The main points that they disliked were: the focus shift from crime story to relationships, the disjointed pieces all over the episode, the change of "atmosphere" compared to series 1+2. the fan-service was not even really recognized as such. Obviously, only active fans will recognize it for what it is and catch all the hints.
So I think, maybe TEH is indeed not the best episode, even if it has great moments and dialogue. I don't think the huge fan service is the main reason. Even without it, I probably wouldn't like the episode much better. (I do like it, of course... but it's the only episode where I skip parts when re-watching, which wouldn't be necessary if it was as captivating as the others, imo)