I love the dark atmosphere surrounding this one, the cinematography is stunning, a delightful contrast to the colourful summery scenes we see in so many of the episodes. And that dance band music that accompanies the killings just gets in your head and stays there. So that's what I liked about the episode. But the killer's motivation was absolutely ludicrous. As has been said, amongst the weakest in the entire series and that's saying something. A shame, because otherwise this would be a classic.