This is on of the Episodes of The Twilight Zone that first comes to mind for me when I think of the series.
One great location, one great idea. It could almost be a stage play.
I guess you could say it's a little slow at times, but I really don't mind that.
Bus stations at night have a feeling all of their own. It's a weird limbo. You're in a time you might never see other than lying in bed at home, and a place you can't really settle. You're tired, but you can't really get comfortable, and sometimes you're sharing that space with the lost souls that again, you never notice in the day.
Then add to that the whole doppelganger thing. It's a piece of folklore that I've always found fascinating and rather chilling. Read about it here:
Doppelgänger - Wikipedia, the free encyclopedia
Great episode, with a very chilling ending. No answers.