I also love the duration of the game. It's like you're watching a film, easily playable in one sitting.
I think the best part of the game is the communication between you and the other player. It was so beautiful interacting with different pitches and movements and imagining what the other player was replying with. I felt like I had made a lifelong friend the first time I played through to the end with my online partner. It was just magical.
This has been my favourite game in a long while.