Are you talking about the Sega Master system game? Thought that was just a standard platformer, it's a metroidvania?
What platform is that on now? Switch?
Also I would like to say Demon Souls, Dark Souls, bloodborne games should count as metroidvania. They are really 3d versions of SOTN structurally.
I wish Konami got their shit together. Can you imagine a real 3d castlevania game in the same style of dark souls.
Have From develop it and it would make bank.
Yes, I mean the Master System game Wonderboy 3: The Dragon's Trap is a Metroidvania - you can get it on Switch and you can even turn off and on the old music and graphics so you can see what it was like in 1989 when it was first released. It's still great. If you do get to replay it and enjoy it, you may also want to check out Monster Boy and the Cursed Kingdom.
I love souls games but I don't agree with categorizing them as Metroidvanias any more than I agree with categorizing them as Jrpgs, which is an argument that happens in nearly every Jrpg thread. My reasoning is thus: I would say the Metroidvania genre is defined in part by platforming and mostly by meaningful backtracking based around power-ups. Meaning that your character keeps getting new moves and powers that make previously blocked paths available for them to explore. So in a Castlevania game when you get a low dash kick attack that lets you squeeze through a narrow hole to access new parts of a castle, that's Metroidvania. In Metroid, when Samus gets the screw attack move that lets her jump over large gaps to find new areas and treasures, that's Metroidvania. And this is why I say Wonderboy 3 is a Metroidvania. When you get the Mouse-man transformation, you can climb up the side of walls in areas you've already been to, allowing you to find new shops and secrets and dungeons. And when you become Lion-man you can enter new areas by destroying blocks that are beneath you using the unique arc of his sword swing.
In contrast, while there is a lot of backtracking in souls, it's not based around power-ups. It's usually just good old fashioned being lost or stuck and having to beat a boss to get a key or turn a lever before you can go any further. You don't get double jumps or air dashes or morph ball transformations that enhance your combat capabilities while also opening up previously unexplorable pathways. Someone might try to argue that getting the lantern so you can see in the dark in the Tomb of Giants is a power-up, but I'd say no. It's an item. It doesn't overhaul your combat options. And it's also not the only solution to illuminating the Tomb of Giants - you could learn the "Cast Light" spell off of Dusk of Oolacile, or wear the sunlight maggot on your head. Furthermore, you don't actually technically need any light, as unpleasant as it would be you can get through the Tomb of Giants without light if you know where to go. The barriers that lock people out of progressing in Dark Souls tend to be keys or levers or something similar, and when they aren't, they're not hard locks like a platform that's too high to reach or a hole that's too small to squeeze through without a new power-up. they're just difficulty spikes that can be overcome, as evidenced by people doing playthroughs where they beat Dark Souls with a soul level 1 character.
So yeah. That's my explanation of why souls isn't a Metroidvania. Now let's talk about why it isn't a Jrpg! /jk
I do agree that 3D games can be Metroidvanias though. There's no platforming to speak of in Arkham Asylum, really, but it's full of meaningful backtracking based around power-ups like Batman's grappling hook or explosive gel, which both also expand his combat moveset. And Metroid Prime has both platforming and exploration that features back tracking using power-ups to find secrets and new areas. Prime proves you can make an awesome 3D Metroidvania game, and Hollow Knight proves you can make one incorporating elements from souls, so I totally agree that the potential for an awesome 3D Castlevania with a souls flavour is there. Konami could make a lot of people happy and make a lot of money if they did it right.