I think for gloomy pigeon and weed infested dilapidation combined with a totally dysfunctional sprawling platform layout, then Perth takes some beating, some of the others suggested in this thread are rank outsiders by comparison. Some platforms are on tight curves whilst the main northbound Highland Main Line one is at completely the wrong height. All are miles away from each other making any attempt at changing trains a long, cold dingy walk.
I agree that the staff are some of the best on the network, and the main entrance area is fine now that the new Costa has opened. But the rest, dear God.
I encourage anyone who never experienced the 1950s to get along to Perth to take a look around, I imagine that this very much what the decade looked like.