Completely agree that the characters have taken over from the plot.
First two series were better as it was about deduction of the mystery rather than Sherlock's angst.
Also agree there was nothing to 'get' it's all very 'this is wacky and mysterious' when there's not actually a thought through explanation to it (so no reasoning through as there was in the first two series - and what made the series good). Hyper intelligent psychopath manages to transport people around Britain and control a high security prison. She gets sad about not playing as a child - all psychopathic tendancies solved from hug from brother.
This lack of thought through explanation is why there's no reason how Watson become unchained. There's none.