Journey is a somewhat difficult game to classify, or even to describe. At the time of its release, I remember reading a handful of reviews all struggling to put into words what makes it such a good game, with their final recommendation only offering the promise that it is, in fact, a good game and that you should absolutely play it. "It's one of those games you just have to experience for yourself." Having now played the game myself, I can't elaborate on it much more than that, other than to say it's indeed a really good game.
Journey is what I guess you would classify an "art game" -- a short two or three hour game with simplistic gameplay meant to tell a metaphoric story through its use of visuals and music. Perhaps what's most impressive about Journey is that it's an art game where interactivity is crucial to the experience; it's an art game that gives the player goals and obstacles that require problem-solving and careful platforming and navigation to surmount. And the experience of making the journey from the outskirts of the desert all the way to the summit of the mountain truly is a beautiful one.