I think it was done better in Super Metroid
That is to me the best platform (/shooter) game in existence. Thinking up new features for a platformer seems next to impossible, after the many years that they have been created it seems like everything has been done before already.
Ratchet and Clank has a very nice idea: you have to travel to different planets and on each planet you can get specific upgrades. On most planets you cannot do something unless you have the necessary upgrade which you can only get on a later planet, so you have to do some backtracking at certain points. I think Odyssey had the same idea with the morphs. That's a very cool feature and puzzle element.
And what else? Super bonusses that are tremendously hard to find (again Ratchet And Clank with the gold bolts). Or what about Kirby who is able to absorb enemies and morph into them?
The N64 Castlevania games have bosses that you have to fight multiple times. Would be fun if you'd create a game where one boss is in your face like throughout the whole game, each time with different attacks. Something like Jenova from Final Fantasy 7, only then with more diversity.
What else, what else... Dark Castle! There aren't enough games like it. You would make me happy if you'd ditch the idea of creating something new and just create a new Dark Castle game with the same gameplay.