1) I muttered 'What am I doing?' many times during the 3ish hours the game lasts. The only onscreen text explaining what's going on is early on, when you're told to hit O (circle) to perform an action. You know you're heading (journeying!) to this mountain peak, you can figure out what the buttons do (the few that do anything) with some experimentation, but that's about it. It's about the thinnest explanation to a video game I can ever remember playing. Yet, the only major problem I had was when I got turned around in snow field for about fifteen minutes. The game is mildly difficult, but it's also very intuitive. Journey is essentially a platform game, and anyone with experience with those will be able to figure it out.
2) 'What am I doing?' is a figurative question too. You're going up on a mountain, I got that part. I'm not sure why you want to get to the top of the mountain. I'm not sure what exactly happened when I got to the top of the mountain. I'm not even sure this was a physical Journey - there's at least a metaphor going on here when your character survive strife and torment to ascend towards the heavens, and then is sort of reborn to do it again. The world is explained, but the character (and all the other ones like) motivations remain unexplained. I guess you live to live.
3) The music is the star of the show; the whole score is great, but it really hit a peak in the last 'level'. The visuals are strong too, better than they were in flOwer (a game with nearly as little explanation.) thatgamecompany sure makes beautiful uses of technology to extol the beauty of nature and bemoan technology. If you are the sort of person who watches play thrus of video games on YouTube, this is might be a good game to watch.
4) I was struck by how smart the computer AI character was - it did a good job of leading me thru levels and even helping me find hidden areas, though it seemed to appear and disappear based on a mechanism I could not determine. That was, until the end, where it's revealed (or maybe just clarified) the other character is really other people playing the game. That was wild. I should've realized it based on their programmed actions, but it felt natural and part of the game, not an extra outside character forced in just to call it a multiplayer mode. It was all seamlessly done.
5) This is short game, 2/3 hours in one playthru. It's a game I know I'll play at least again, partially to gather trophies and partially to see what I missed when I was so puzzled by the first time. If you liked Flower and Flow, it's definitely worth $15. You may want to wait for it to go on sale again if you weren't as in to those games, but it's a good $10 for a light weekend game.