I packed my pipe, brewed some tea; and put on the stream for BBC (mad rhymes, I know).
At first I liked it. The setting and the atmosphere was really nice, but slowly and slowly it became more annoying than anything. Especially with the 'twist' (which was basically hinted several times by the wall breaks) it just lost its value to me, and the conclusion of the case came literally out of nowhere. We got to see some cameos every now and then, and whatever we got also got killed by that 'twist.'
I wouldn't go as far as calling it terrible like @carbonmated, but it wasn't what I expected. Although, nothing even close by any means.