I just played this game my first time yesterday, loved it. Although, I will agree with most reviewers that the rules are a bit intricate in the minor issues. So, as I hope to play a second round tomorrow one question arose in my mind. Does a completed stairway (or hallway) count as a completed room for scoring "most completed rooms"?
Yes, Corridor rooms (including hallways and stairs) do count for both the Favor and the Bonus card that give you points for completed rooms. (Obviously it's difficult to complete a hallway, but it can be done by placing another hallway on each side of it and a room at each end!)
But note that the Favor and Bonus card that give you points for external entrances both explicitly state that Corridor rooms do not count for them.