I am going to put lots of good words about this game, because it really deserves them. You should definitely tag it as an rpg, because despite very limited locations it is an rpg game. The fact that even strengthens this statement is that as you suggest the game is not linear.
The best way to play this game is to begin in the evening to feel the atmosphere of running through the night with the more and more complicated game plot. At one moment you are really starting to feel the heavy atmosphere of the city, feel the pain of existence of people living in it. Ever heard of the writer Thomas Pynchon? In the game you can feel something like the heavy atmosphere of one of his famous books, "Crying of lot 49". I could also compare this game to movies which action is taking place during one night, even only few hours, like "Collateral" for example. The game is great. Absolutely great.