This Moffat quote is phenomenal:
"The reason we still have Benedict and Martin is we still give them acting challenges. Otherwise they wouldn’t come and play with us. They don’t need the money. What we give them in terms of money isn’t something they’d regard as a significant fee anymore. We’re making this in a shed in Wales. We think really carefully about giving them something to play because they’re both amazing actors. Normally if you watch a show, [the characters] tend to narrow as the people who make the show tend to know what works. When I was doing series 3, I went and looked at Martin and Benedict’s other performances to remind myself of what else they do. I watched the British The Office again."
And that's the Gold Standard...that's how you keep operating on a high level. If you operate with a higher standard then "normal" that instantly renders all critics powerless. Fresh.