The first two episodes are great, lots of subtle camera work and background detail that really build that sense of dread. Unfortunately, what could have been a brilliant 2 hour film instead becomes a 9 hour slog. Without going into spoilers, there are so many storylines that often take up entire episodes and have absolutely no bearing on the ending.
Another quite distracting point is that the series is supposedly set in 1980's England, but feels nothing like it. Half the characters speak and dress as if they're from the 50's, the other half from the present day. The accents are pretty poor as well, with one character constantly switching from American to Irish. Slow burn horror can be incredibly effective, but in this case it's obvious they didn't have enough story to pad out the run time, so the end result is just plain dull.