Hyrule Castle is such a cool area, definitely my favourite part of the whole game. It feels almost Metroidvania like. I've felt a little disappointed, not so much by a lack of dungeons, but a lack of aesthetic variety that you'd usually see in the dungeons of the Zelda games. The overworld is very varied and discovering the different themes of the areas early on was something I greatly enjoyed, but the Shrines and Divine Beasts all look exactly the same, the puzzle design is exceptional, some of the best puzzles in any Zelda game, extremely creative, but it always takes place in the same place. The only expection to this being those overworld puzzles and challenges that opened Shrines, they're good, but needing to go into a shrines to get your rewards felt a bit pointless.
Anyway, Hyrule Castle, it had an interesting aesthetic of a wrecked castle, a corridor design that could still be explored in a non-linear fashion, it's great.
I'm wondering what they could do for the next big Zelda game, I think another open world set in Hyrule (as the know it) would be far too iterative. I'd want to see them do something way different allover again. Which bring me to Hyrule Castle, because I'd honestly be really happy if they make a Zelda game with the world design similar to the level design of Hyrule Castle. I'm trying to explain this without mentioning any certain other games because I know Zelda fans get annoyed when you compare Zelda to other games lol.
Even though this is one of my favourite open world games, and the open ended systems praise the openness of the game, there are certain somewhat more linearly designed parts like, before Zora's Domain, Death Mountain and Hyrule Castle that also worked really well with the open ended systems, maybe another Zelda game could take a greater look at that, the older games did do this in many ways too, but without the open systems of BotW.
Breath of the Wild, though, brilliant game. My favourite Zelda is still Majora's Mask, but I'd say this is second place now.
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