Babel gets high marks from me in every way -- the story is compelling, the prose is beautiful, and the puzzles are well woven into the stoy. You are thrown almost violently into the world of the Babel Project station from the first sentence; while it's only a short-to-mid-length game, the sensory details will linger disconcertingly in the back of your mind for days afterward. It may be cliched, but the amnesia/flashback device is played here masterfully.
Every detail and every puzzle in this game is there for a reason; the player isn't made to jump through hoops just for the sake of mental exercise. Why are the keys to routine parts of the station so hard to obtain? By the end of the game you will know and it will make sense. The writing also gives an overwhelming sense of urgency while not, as far as I could tell, actually having a time-limit coded into the game (other than in one puzzle, which you can do over if you mess up). This makes it very playable for relatively new players apt to go over and over things like me.
No character in this game is morally unambiguous. They are human, fallible, and very believable. Some scenes do stray just over the line into melodramatic or preachy, and the romantic subplot seemed a bit unnecessary to me. But that's only a tiny quibble in what is otherwise a seamless and chilling story.