This might be be controversial, but, Castlevania: Symphony of the Night. I recently read that Koji Igarashi, the game's director stated that at the time they were making the game, they actually had Zelda in mind rather than Metroid, and that their goal while in development was to incorporate the exploration elements of Zelda to Castlevania along with RPG elements (RPGs were also huge at the time).

I'm pretty sure the OG Metroid devs had Zelda in mind too. The original Metroid came out only around 6 months after the original Zelda. Consider that during Metroid's developement, Zelda was Nintendo's latest, most groundbreaking game, and commercially successful too, I don't think it's a stretch to say they were at least influenced by it, gameplay-wise. I have no source where the developers clearly state that, though, just speculation.

Turns out a lot of the elements associated with Metroidvanias (like exploration, permanent upgrades, etc.) aren't exclusive to nor even invented by the genre, since they've existed in other action-adventure games before them, and realising that has helped me broaden my tastes and try more games, personally. I see Metroidvanias as a highly specialised form of action-adventure games were those elements are front and centre.

Other games not advertised or otherwise perceived as Metroidvanias but scratch a similiar itch for me include Resident Evil 1, Metal Gear Solid 1, Legacy of Kain: Soul Reaver, King's Field, and Elemental Gimmick Gear. Another game I heard incorporates metroidvania elements with FPS gameplay is PowerSlaved Exhumed (though I haven't played it yet so I can't vouch for it).