I feel a bit bad for IGA here. Like, I'm sure he doesn't just want to straight up copy and paste SOTN's biggest twist (plus some people will call him lazy if he does) but a non-insignificant number of people are probably going into this game expecting an inverted castle too. Between a rock and a hard place I feel.
I don't want him to repeat it, but it'd be nice if there was a secret that unlocked more of the game if you don't get the 'bad end'
Also I wonder how the map will work and how map/item tracking will be.
Super metroid would give you a dot to let you know that there was an item in the room, but the dot would stay whether you picked up the item or not. Hard for you to tell whether you need to backtrack to 100%.
Metroid fusion and zero mission let you know you picked it up. It would be a circle if you still hadn't found it, or a dot if you had. It was a godsend.
Then axiom verge, this year, had none of that, so it was tough to determine if you needed to re-explore a room. Instead, it would tell if you if you found all the items in a zone or not by using a yellow dot. Purple dot let you know the map was 100% explored.
Basically, I loved the circle > dot from fusion, and wish more metroid/vania games used it.
When you reach the top of the tower in the first castle and beat the "final" boss, you learn the tower is actually a rocketship that takes to you to the MOON Castle where you have to fight Space Dracula!
I've always had this idea for a really good '2nd castle,' which is basically that you time travel back to the beginning of the game w/ all your powerups and upgrades and you can now traverse to areas sooner than you should be able to, and the enemy placement is entirely different and all the bosses are in different forms (maybe a moth boss is still in its coccoon, or an evil scientist hasn't finished his potion yet, so he turns into a different monster, etc). And by going out of order, you actually 'fix' the future and prevent yourself from getting sent back in time. Maybe during the normal story, a portion of the castle burns down, so you explore its charred ruins, but if you get there early enough, you get to see what it was like before it burnt down and prevent it from getting destroyed, etc.