It's fun to be a parrot!

This is a wonderfully made game, and deserving of the praise it gets. "Beautiful", "visually stunning", "enchanting music" etc, yes yes all true but you've seen this in other reviews. That out of the way, let me share a few thoughts about the game.

1) It is primarily story driven. And the story is quite moving with the characters both living and dead having fully fleshed out personalities. All 'challenges' as it were to completing the story are very easy, and I believe even the most casual player will enjoy playing. Children, older folks, you name it. Playing solely for the story will only take 5 hours or so.
Be ready to feel emotions.

2) Getting all the achievements will be time consuming. And this, btw, is THE only complexity in this game. There is no fighting, rushing lanes, or complex control schemes. There are 'mushrooms' and 'relics' one collects while exploring, and while the relics flesh out the world in a way, the mushrooms are just for finding. Some of these will be very difficult to find.
I recommend playing through the story first before searching for all the extras, if your goal is 100%.

3) The game performance, stability, controls, and presentation are all AAA title quality. I played using an xbox controller and it was great that way. There were a couple times I got "stuck" in geometry, and had one crash, but these were very, very minor issues for an indie game this polished.