I want basically everything Sherlock said in this episode on a T-shirt.

My personal opinion on this is that during his absence after TRF Sherlock realised he was lonely and he missed his friends. We know little about the time before PINK, but obviously he wasn't very stable before he met John. It seems that he had more contact with Mycroft back then.
Now that Sherlock is back in London, he wants everything to be like it was before TRF, because that was the best situation from his point of view. But things have changed. Everyone has boyfriends/girlfriends, which is a thing that Sherlock isn't really interested in. And as both Mrs Hudson and Mycroft keep reminding him, when people are in romantic relationships, it can happen that they leave their old friends behind. Especially after getting married, especially when they have a family of their own. That bothers Sherlock, and that's why he's very stressed.

Another thing - there's this repeatedly occurring allusion (I don't know if it was mentioned elsewhere, couldn't read all the threads that quickly). "Elephant in the room" is an English metaphorical idiom for an obvious truth that is either being ignored or going unaddressed. The idiomatic expression also applies to an obvious problem or risk no one wants to discuss. It is based on the idea that an elephant in a room would be impossible to overlook; thus, people in the room who pretend the elephant is not there have chosen to avoid dealing with the looming big issue. (from Wikipedia). I think this points to the existence of a clue that Sherlock has overlooked because of his emotional stress or whatever, probably something to do with Mary. As the trailer to HLV also said Sherlock makes a big mistake.

Perhaps he's a bit insecure internally. Not about his work, but about himself as a person.

tobeornot221b wrote:

The only thing in the episode that is so NOT Sherlock is that he doesn't go once by taxi.

 
True. He'll have to do an extra taxi ride in the next episode to make up for it.

SusiGo wrote:

And there is a difference between deducing people during a case or for fun or showing off or evaluating emotion when he himself is concerned. He knows that he hurt John more than anyone else and therefore it is more difficult for him to confront him than Lestrade or Mrs Hudson. I think we all know that he does indeed have feelings which becomes quite clear in his conversation with Mycroft. 

As I wrote somewhere else Sherlock uses trial and error to get through to John. First he tries comedy which does not work at all. Then there is his heartfelt "sorry" after his parents have left. But he still needs to hear John say he forgives him and so he comes up with the "We are going to die soon so let's tell each other the truth" in the train. It is completely weird but this is Sherlock after all. And his laughter at the end also has something slightly hysterical, tinged with relief after enormous tension.  

For me the scene on the stairs in 221B is the true reunion. His "I heard you" and the fleeting moment searching for words is what I waited for. And then they are ready to face the world outside. 

 
Yes. And I think that his/their laughter in the train breaks the ice somehow, even more than the "I forgive you".
And as we know, John loves a bit of danger. I think after Sherlock has found the off-switch, he calculates that this wouldn't be a very impressive ending to the scene. John would go home a bit disappointed - oh, well, we were confronted with a bomb, but it had an off-switch, nothing really exciting happened and I'm still mad at Sherlock, perhaps I'll better stay at home next time ... So Sherlock puts up a little show. And it works. As Susi said, completely weird, but that's Sherlock.

Being Sherlock, I could imagine him being in pain and just not letting it show. Anyway, the torture scene was bad. I so wanted someone to hug him to make up for it a bit. At least Lestrade did.

What would you give Moriarty for Christmas (if he was alive)

A nice juicy APPLE
A BIG kick
A CROWN
A DENT
An ELEXIR of life
A FRUIT BOWL for all his apples!

A great GAME
 

Have a good time, Harriet.
And see you soon, Ormond Sacker. It has to be difficult to abstain for such a long time.

A third option like "other" or so (at least) is definitely missing here.

Good! I'm looking forward to it.