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?
After playing it for 2 minutes there are clearly two kinds of obstacles that could only be surmounted by some kind of enhancement. And there's a Metroid-style grid map you can bring up.
There's nothing useful about this kind of negative comment.
If the maker wants to advertise his little game as a metroidvania and the first impression is that it seems like a simple platformer then the metroidvanianess isn't obvious enough and there's room for improvement. If you've made the game yourself you can become blind to little things like this and it's very useful that someone points it out.
"Negative comment" my ass. It literally starts with the words "great work". That's a clearly a supportive comment.
I wouldn't say it was a negative comment but I also wouldn't say the comment's assessment was correct. "Nothing Metroidvania about it" is plainly false. "Typical run and jump platformer"... wouldn't agree there, either. This is closer to Metroid or Castlevania than say, Donkey Kong or Super Mario.
Even the atmosphere. It had - dark themes, 'creepy, dungeon' music, Skeletons, Spike traps, Spiders, and the Map screen we've seen since SOTN.
Lastly, you can start a comment however you like that doesn't make the comment that way. I could say, "Great work! For a worthless pile of garbage like yourself" and I don't think anyone could argue that because I started off my saying, 'Great work' that the comment was positive, maybe that it was supportive! (But again, I don't think the comment was negative, no matter how much I disagree with it)
What do you think is missing for it to be called a metroidvania?