An amazingly good game, with a fascinating story and good gameplay, that does the right things in the right places. But.
I still don't know if I liked the game or not.
The story in Bioshock (no spoilers) is deep and engrossing and thought-provoking...and sad and disturbing and heart-wrenching. If I were judging this game only on gameplay and graphics, it would still be a 9. I am not, however, as I believe that it is the story that holds the game together for something like a BI. And it's still a 9, even though I don't know that I liked it, because that story was so intriguing and well-done that it created an emotional response (the goal of all good stories), even if it wasn't entirely positive.
Is Bioshock Infinite a "must play?" I don't know.
Am I glad that I played it? Yes.
Will I ever play it again? I will have to wait and see.