So I now have the stuff needed for the good ending, but I haven't beaten the final boss yet. My thoughts:
This game lives of two things, exploration and boss fights, and I feel these things work well in mid game. Early on the game is quite slow and you lack abilities which blocks the exploration. After making it to City of Tears, I felt I had enough mobility and combat abilities that I could access the game properly. From there to the dreamers the game really pulled me in.
The endgame felt poor in comparison. Getting the bad end after finding the dreamers was pretty trivial but fine, whatever. If I didn't know about a good ending, I would have stopped there. I had already explored all the obvious paths on the map, so natural exploration was pretty much over at that point. I knew I have a bunch very difficult bosses I can fight, but honestly I was feeling quite bored of fighting. So in the end I just looked up what I need for the good ending. Turns out some of the hidden bonus stuff is just way too obscure to find on your own in a reasonable time.
I guess the endgame is fine for people who want more boss fights, but I felt I got to beat enough people on the way to the bad end. I really liked the 1 on 1 fights like Hornet, but some of the bosses (like those who spawn stuff) pretty much came down to having good gear. Those were either really hard or really easy, but not very satisfying.
In general though, I did like how you could find difficult bosses early and come back to them once you had buffed yourself properly. It allowed me to adjust the difficulty by choosing when to engage in a fight. This doesn't work in the end/postgame, since I have little desire to search blindly for more upgrades in an apparently complete map. And the remaining fights are too difficult and too inconsequential for me to care.
I think the game could benefit from a couple of structural changes. First, one could do a full BotW on the Metroid structure and just give the player all the mobility upgrades in the beginning. This would open up the world for exploration faster. The game could still gate areas behind tough bosses. Secondly, I feel the endgame needs more direction and natural progress. Either something else than a bunch dudes to fight or keep the dudes but also have an interesting way to buff the Knight more so that I can adjust boss difficulty like I could mid game.