Love me some Metroidvania! Probably my favorite genre of games.
Super Metroid is the best. So good. As are Metroid: Fusion and Metroid: Zero Mission (but Super Metroid takes the cake).
Castlevania: Symphony of the Night is the best Castlevania one. The GBA and DS entries are also quite good. But the 8-bit and 16-bit entries aren't Metroidvania.
As for non Metroid or Castlevania ones:
Shadow Complex is awesome and has a different feel than most since it's set in modern times.
Ori and the Blind Forest and Ori and the Will O Wisps are gorgeous, hand drawn looking graphics set in a mystical forest.
Cave Story is a fun little Metroidvania with a retro 8-bit feel.
The King's Field games on PS1 and PS2 are first-person RPGs that definitely have a Metroidvania, exploratory feel to it. Though it's one of those games you either love or hate. There's no in-between.
People don't really think of Zelda games as Metroidvanias, but the design is very similar. You get that one item, such as a hookshot, that now allows you to get to that area you couldn't get to before.
Though unlike others here, I didn't like Hollow Knight. Just didn't grab me.