Journey is the first game in as long as I can remember that I've played from beginning to end in one sitting.
It offers such an ephemeral experience that any preview would be pointless; any review would spoil too much.
Thus, instead of directly discussing Journey at all, I'd like to say only this:
Does the question "What if Jason Rohrer joined Team Ico?" get you giddy?
If so, then Journey is probably worth your $15. Go in blind, and enjoy the ride!