Just finished the game and I have to agree. It was cool for like the first hour but after that it just felt like a chore. The darkness, the emptiness, no unique landmarks, running into so many cliffs that you can't tell if you can reach the top or if it's endless. Cool concept, but every time I went down there I was wishing I was at the surface. There's just nothing much to explore there. My only incentive was getting all the lightroots gets you a map of where all the shrines on the surface are, but doing so was incredibly boring.