It was brilliant, I loved it. A few things bothered me of course.
I'll start with the crime: an underground train-bomb blowing up the Houses of Parliament... A Guy Fawkes inspired storyline is fine, but it needed to be original, this reminded me way too much of V For Vendetta. The deus ex machina solution also bothered me a bit, just switch the bomb off? Really? Come on now... The crime/mystery wasn't the important thing about the episode though, the centre piece was Sherlock and John's reunion and it's aftermath, quite right too. A more realistic reaction from John Watson than the one we got in the canon, but not completetly over the top, just the right amount of violence . DI Lestrade's reaction was brilliantly simple, "Oooh, you bastard!" and a hug, love it. And Mrs Hudson's reaction was hilarious, she should've hit him with that pan though, a missed opportunity .
"The Empty Hearse" or is that the "online fandom"? And the multiple theories/fantasies in the episode, a courteous nod to the fans or a sly dig? I prefer to think the latter.
How he did it... Even if it isn't the real one, I'm completely happy with Sherlock's reveal to Anderson, everything slotted into place nicely. I don't understand how some people can be disappointed with it, like Mark Gatiss said at the Comic Con panel, "The important thing to remember is; there really are only a few ways you can fall of a roof and survive, it's not Black Magic, alas." Looking at some of the reactions on Twitter is beggar's belief, I don't know what they were expecting to see. A thing that did bother me about this though was the fact that Sherlock and Mycroft new all along about what Moriarty was doing, it seemed like a bit of a cop-out, should've elaborated a bit more on that.
The stand-out for me was Mary Morstan, brilliantly played by Amanda Abbington. I found her intriguing and I agree with previous posts that there's something not quite right with her, I like the idea that Magnussen is somehow involved.
A great start, very excited for the next episode.
Mycroft.