Sure.
The world is packed with lore, much of it optional. You get no real gameplay benefit for visiting these. Similarly to Metroid Prime, there are deeper details of the story housed in these, things that flesh out the background of the world and provide history. It helps it feel like it existed before you entered the story. A lot of it is meaningless, sure, but again, it's optional details for those who want to dig more deeply into the world.
I kind of don't even understand this one. I would have liked more secrets, but it wasn't billed as open world or free-roaming. It's a linear action game. Seems like his expectations were off here. Silly complaint, honestly.
I don't know what puzzle he was talking about...? It's a pretty straight forward game with no puzzles. The final boss battle is definitely a slight departure, but makes sense in the context of the story. Also, I thought it was a pretty cool event, so I think we just disagree there.
As for the ending, I'm not at all shocked he didn't care. He didn't like the game. I am shocked, though, that he says couldn't comprehend it. It wasn't a very difficult conclusion to understand, and makes sense given the events that lead up to it.
And as for you insinuating that people love the game because they're buddies with Kassavin, I loved both this and Bastion and I am not buddies with him. I've spoken with him at shows and demoed his games, but outside of those experiences and a few press emails him and I are entire strangers. It's a pretty presumptuous accusation to make, and you might want to think better of posting things like that in the future.