I think the thing that feels closest to the truth in this thread is that it's an image problem. Metroid doesn't attract people, not because it doesn't have the same appeal as other Nintendo series, but because its appeal isn't conveyed well and is relatively difficult to get without playing it yourself. I'm not sure Nintendo knows how best to sell Metroid. Dread is titled and marketed like it's a horror game when it's really not at all. I feel like they know why people actually like Metroid, but they don't believe that can sell it. A quiet trailer scene with no action depicting Samus emerging into an environment like Phendrana Drifts would do more to accurately communicate its appeal than probably any commercial or promotional image Nintendo has ever done. "First person adventure" kind of gets made fun of, but it's probably the most incisive piece of marketing Nintendo ever did for the series, and less of a buzzword than calling Breath of the Wild an open air game.
What's weird for me is that I generally prefer fantasy over sci-fi. But Metroid has this hold on me that no other game series does. Despite my love for grand adventures, I find the moody, introspective elements of Metroid pulling me back time and again. And I kinda like that I'm part of a minority with similar tastes. I only want the series sales to explode so Nintendo will be forced to make more.
I was beaten to it, but this also kind of reminded me of the whole "Star Wars isn't really sci-fi, it's fantasy in space" thing. The games are really big on ruins and artifacts, across the series you spend far more time in caverns, jungles, and ancient temples than you do in any "futuristic" settings. Even the two games set entirely on space ships are set on ships specifically dedicated to artificially imitating the same sorts of environments you'd see in Donkey Kong. Samus repeatedly encounters ghosts, magic is canon, and her nemesis is literally a dragon; complete with the archetypal fairy tale role of being the most prominent obstacle but not actually the big bad. There's also the (very funny) observation that Samus is technically a magical girl, based on the way her abilities work. Her suit runs on willpower and materializes with a thought.
I don't really get why people keep bringing up sci-fi as an issue though. Is there actually some kind of known stigma there? I would have definitely guessed that up until recently sci-fi was more popular than fantasy. Star Trek and Star Wars seemed to loom over pop culture in a way that no fantasy series really did until the corps managed to start making "nerd stuff" fully mainstream in the 2010's. It was kind of weird to live through the popularity of Game of Thrones and hearing my mom talk about dragons, similar story with Marvel. This stuff reached people who never cared about Lord of the Rings.
That being said, there is something to be said about how sword and sorcery just seems more popular in the indie space. I feel like the amount of Symphony of the Night clones or Souls clones is fairly disproportional to the Metroid clones. Part of that I think is just those formulas allow for level ups, which allows for consistent progression, and thus consistent dopamine. Which is extra funny, because Igavanias were not actually nearly as popular as Metroid. I'm pretty sure the only ones that passed a million were Symphony (which was never confirmed in it's original run, we just know it sold 700k+ in Japan and the United States combined) and Circle of the Moon, which isn't even an Iga game.
This is likely down to two things: the Metroidvania genre comes from SotN, not Metroid; and an Igavania is
far easier to make than a Metroid. An Igavania will invariably have like less than ten progression upgrades in the entire game, and the only Castlevanias where they're even the main thing driving progression are the Sorrow games. Portrait and Order are more level-based, and SotN and Dissonance are more open. They're also almost always glorified keys or comparatively very simple mechanics like a double jump. The first progression item in SotN is literally a thing that lets you open blue doors once you have it. Most of the later ones like mist or spike breaker are needed for two or three rooms and don't really have much purpose or functionality outside of those spots. Metroid, like Zelda, puts the
Action in Action Adventure. Missiles don't
just open red doors, they're an integral element of the game's combat. You can master using missiles, whereas there's never much to master with most of the abilities in other Metroidvanias.
Now, progression aside, Igavanias do like to give you a ton of different potential items and equipment you can use which are largely optional, but this is more or less a gimmick. They aren't all equally viable or meant to be equally viable. The vast majority of weapons in SotN are worthless; on the other hand a few are completely broken. Both Sorrow games have an entire stat that doesn't even work. The whole concept is very messy and a crapshoot on whether or not something you picked up is effective at all. Every item in a Metroid game has a considered effect and functionality and is guaranteed to be an improvement to Samus's capabilities, even if incremental or unneeded. And that's not even getting into the level design and how Metroid areas are these big mazes that require you to find hidden passages to progress, whereas every other Metroidvania area is basically just a bunch of hallways with enemies and maybe there's some fake walls hiding an optional secret room here or there.
I suspect this is because it's way easier to make something that has more room for error on the part of the
designer as much as the player, which is why there are so few old platformers that play similar to Mario even though with its popularity and influence you'd think they'd be endless. Imprecise level design and game balance become less of a problem the more wiggle room mechanics you add. Mario has to be very precisely designed to work at all, but add a sword slash and a health bar and remove the complicated and nuanced physics for running and jumping, and you have a character that can more or less take whatever random assortment of platforms and enemies you throw their way.
