Awful as Moriarty
His interpretation of the character is so needlessly over the top and campy to the point where watching Sherlock becomes quite difficult.
Just a terrible actor.
Just imagine to have an enemy who's really over the top like Moriarty is - can you imagine anything more unpredictable and frightening?
Except no-one is frightened of a Graham Norton impersonation. It's exactly the same mistake the BBC made with John Sim's Master in Doctor Who - by turning him into an over the top, wildly overacted clown they completely dilute any potential for menace or to be taken seriously. Worse, the actor completely departs from anything like genuine human behaviour - even people who do have violent mood shifts - to just remind you that's he's Acting with a capital A, dahling - aren't I just so, so divine? It's just a very fake, unconvincing performance rather than a flesh and blood character. He's really very predictable (it really is basically a rerun of the Master, presumably via the Steven Moffat connection) and rather than frightening in any way merely annoying.
"Security - release the badgers."