I'm going to call bullshit, right off the bat. "His Last Vow", really disappointing. Besides the "why can't we have nice things for once" plots twists, the end just doesn't make sense (even in a way of "ZOMG, and the fannish fanning over the end, you won't believe the hype").
The plots holes in this episode are so wide there's no gauging them. Besides committing the sin of "withholding information from the reader/viewer" serially in this episode, the quick varnishing of Mary being the leverage to get to Mycroft doesn't explain how Jeanine is Magnusson's assistant and Mary's Maid of Honor. As explained in the previous episode, "Sign of Three", the universe isn't so lazy as that.
And then there are 3 very plausible chances to kill Magnusson (which is clearly where all of this is heading) without leading to the forced error ending of shipping Sherlock off to sure death in Eastern Europe. The delay Mary has after disabling all of Magnusson's security - which, BTW, wouldn't that have also tripped the guards to gather Sherlock in the lobby since the big guy was already up top? - is just bad writing. If Mary is who they tried to portray her as, Magnusson would have been bleeding out by the time Sherlock and John got through the routine of checking the other bodies. No, really, pros don't linger and give long speeches (doesn't anybody read the Evil Overlord list?). As Syndrome says in The Incredibles, "I don't believe it, you got me monologuing." Yea, people don't do that. I blame James Bond. Anyway, Sherlock surly went to Magnusson's to kill him (he makes sure John brought his gun, why didn't Sherlock bring his own gun, though, he has one). Why didn't he do this as Magnusson is showing off his master plan (again, read the Evil Overlord lists) sitting in his special room (all the pieces are revealed right then)? And why John just didn't blow Magnusson's head off after the first flick, I'll never know (because, after all, he's in love with Mary, has already dedicated himself to protect her, and this asshole in front of him is both distracted and being an asshole, John already has shown himself capable of sudden violence).
And then there's the end. Really. Are we going to pull that trick a second time? So I'm going to guess here that it's someone else using Moriarity's image and reputation (after all, the voice is completely different, as exemplified by the final cut). Also, Moriarity was not a publicity hound. He works in the shadows, that's his MO. The pubic doesn't know who he is. He's not interested in generic terrorism (which this message clearly is), he is also about leverage and the pressure point. And there's really no way for Moriarity to come back. There was a conspiracy to help Sherlock, Moriarity was alone on that roof. Blanks? Sorry, even blanks fired inside the mouth will kill you (don't try this at home, take my word for it). There is a possibility that shooting yourself (or being shot) through the skull can leave you alive. It's possible, except for what happens when you shoot through the roof of your mouth with the gun in your mouth (there's a lot more damage than just the bullet, which is also why firing a blank in your mouth will kill you as well). Plus, Sherlock, our master of observation, watched him die. If it had been some trick, don't you think he would have noticed? Plus, pulling one character back from the veil may be acceptable, two or more become the "Pamela Ewing discovers
I could accept the rest (drug den to get at Magnusson, which then sort of dies on the vine, Mary being an uber-secretly deadly assassin trying to make good, all the coincidences, and drugging everyone on Christmas), but that last one just tossed me out of the story. If this is actually a return of Moriarity, I have to call bullshit. Also, I have to call "lazy writer syndrome" (which is a shame given the rest of the show).