The metroidvania inspirations are pretty clear, it's a large map that you unlock gradually by finding abilities on the map. Including some back-tracking.
What do you think is missing for it to be called a metroidvania?
The graphics and scenery. It's 13 kilobytes of JavaScript with no bitmapped graphics in it, I know, but if we settle for (as an example) your two very broad strokes of running back and forth and unlocking new areas then hundreds of old NES and SNES games have suddenly become Metroidvania, despite nobody ever branding them as Metroidvania.
I don't mean to come off as a retro-gaming connoisseur, but there's a certain feel and atmosphere to the Metroidvania branding - it's more than a sub-genre - and it shouldn't be taken lightly.
I'd say that, particularly in modern genre terms, "Metroidvania" refers to a game involving gathering abilities that unlock new areas, with either mandatory or optional-for-bonuses backtracking to previously blocked paths. (This is distinct from just flipping switches or finding keys -- you have to find things that change your character's moveset, and the new capabilities are what let you pass through.)
Non-linearity and ability-acquisition are the only essential elements. There's often platforming, a certain isolation-vibe, and a large single map, but those aren't mandatory to get the label.
Admittedly, that definition as given leaves most Zelda games qualifying. You go around gain abilities, there are often optional rewards for backtracking and using those abilities. (BOTW is a pretty major exception here, and so are the NES zeldas).
One notable difference is that there is rarely benefit to backtracking into previously completed dungeons. Even for 100% it is often possible to get everything with the first pass (without even using glitches or unintended interactions), which is not like most metroidvanias. However, most Zelda games but the games do tend to favor overwold backtracking for optional rewards.
Zelda, Metal Gear, Wizardry, Faxanadu, Rygar, Ys, Mother/Earth Bound. The list goes on and on. The element of revisiting previous stages/locations to unlock portions you couldn't access earlier on was a basic ingredient of old adventure games.
Spanish wikipedia, while English wikipedia says something else. Did you hunt with Google until you found some lone source citing it as "Metroidvania" just to try get a point across?
I live in a Spanish-speaking country, so Google defaults to Spanish Wikipedia. I forgot to change it to English like I did with my second link for the HN crowd. But you are incorrect yet again. https://en.wikipedia.org/wiki/Rygar ctrl-f "Metroidvania"
My point is that you create a lot of noise when your "corrections" aren't actually correct. It's basically nerd sniping to be wrong on the internet, especially about games.
Yes, I'm contributing to the noise. But I'm correct, so it's okay according to unwritten HN guidelines.
What do you think is missing for it to be called a metroidvania?