I can't think of a single mystery box format that ever outdid a gimmick of the week/gimmick of the to-be-continued. Even the X-Files, which tried to hold a tighter narrative arc, was better in its monster of the week episodes.
Only fully planned arcs like Babylon 5 work.
Matthew Best
Davies half-assed mystery box bullshit was a relic of a bygone era, and every payoff landed with a dull thud.
They brought him back to save the show but all he did was kill it faster. I dunno what happens next with Doctor Who, but given the state of the BBC the answer might be "nothing."