I rewatched the episode, and must have caught it in a better mood. It's a decent show, with good writing and good leads. The last episode suffered from trying to move at a breakneck pace, which diminished tension and, to some degree, clarity. If there had only ever been one woman in one car reading from her blackberry with C4 strapped around her waist, then I think the episode would have been stronger.
And Moriarty just wasn't good. There is no avoiding the fact. I can see that Gatiss wanted to slightly reinvent him, making him more manic in line with The Joker and the latest trends in supervilliany. But it felt cheap, partly because the actor lacked the talent to achieve the desired effect, partly because such a generic arch villain seemed an anticlimax after all that build up. I join with those hoping that this Moriarty is just a stooge standing in for the real deal, played by someone like Timothy Dalton.
Still want to see the whole show taken to the provinces, for Hound of the Baskervilles meets Withnail and I.