Clearly not *the* bleakest, but for stations with 1 million+ passengers a year, Cambridge North is pretty bleak.
Everything is drab gray, no colour or character at all, except for the Wolfram-inspired 'Life' patterns that really only serve to let wind and rain in. Almost no facilities, no ticket office, one side of the station blocked off with a huge fence that often has many unhappy-sounding dogs barking on the other side. Vast quantities of CCTV cameras for some reason (there are at least 12 (!) cameras on the short overbridge alone, goodness only knows who thought that many cameras were 'necessary'). Once you leave the station you're in a large open windswept concrete square with almost no civilization to be found within a five minute walk in any direction, bar an isolated hotel, an isolated office building, a fairly rubbish Co-op that opened recently, and the occasional speeding cyclist trying to run you down. Oh, and more recently 2 (!) overpriced kebab vans which appeared within weeks of each other.