I've mentioned this game before recently, but I just finished Gris and am absolutely smitten in a rare way. It's very short, simple, and relaxed (no fail states), but it's got probably the most beautiful art direction and score I can remember. That being said, it does also wind up doing some pretty interesting things with its simple mechanics too.

You can finish it in a few hours, but there's a draw to return again just to sink back into the world, cause... It's just pleasant there.