This one succeeds for me almost entirely on mood and atmosphere, on being unsettling, keeping you uneasy for reasons you can't really put a finger on, but then I'm pretty biased, as those are the things I love most in a scary story, and focus on in my own ventures into the field. There is a tinge of dissatisfaction with the lack of a clear explanation, but I'm mostly at peace with it.
Particular props to the director. The direction throughout the series is strong, but this is the standout in that department for me, restrained, fluid, wonderful use of subtle movements, but not afraid of dramatic, angled, Hammer-esque close-ups to really play up the pub bait and switch.