Lovely game, and if you get a good companion one of the most friendly gaming experiences you'll ever have. This was pretty much the reason to get a PS3, now a lot more accessible.
Hm. When it was released in 2012, the fact that it's cooperative multiplayer was actually a secret; you had to discover this, and often led to people abandoning their "NPC" who then had a rougher game. So I'm not going to spoiler-hide that. Find your friend and help each other.
I've replayed it several times now, sometimes being a better guide to a companion, sometimes just wandering around and exploring every nook and cranny. I think I have all the 'cheevs on PS3, or very close. It's unfortunate that it's such a short game, 8 zones and done.
Their prior games, Flower and Flow are also lovely, but much less engaging. I haven't started Sky yet, I may wait for the Mac version.