I have to disagree on both accounts.

Even the first game that coined the the term metroidvania (which was Castlevania: Symphony of the Night, just in case you don't know) required fighting a lot more than precise jumping. Thus calling it an action game is more correct than calling it a platformer, since in platformers you typically have little capability to fight but are required to dodge or jump on enemies.

And even SotN was only 2D because of the date it was released. Later games in the Castlevania series were 3D as well. Look up Lords of Shadow 1 and 2. If you exclude the series that defined the genre just because you don't like 3D then the term metroidvania means nothing any more.

On top of that there are actually quite a few 3D metroidvanias, even if you don't know them. On top of my head I can at least think of Shadow Man, the whole Legacy of Kain series (except the first game which was also 2D because of its age), the whole Darksiders series (except the spin-off Genesis, which was isometric) and Lords of Shadow 1 + 2. I'm sure there are actually a lot more that don't come to mind right now or that I don't even know.

"platformer" has been used for games with significant amounts of combat, including the Classicvania games.

Specifically, Metroid Prime and most of the Metroid games after that.

Thanks for the history. I admit I never played any Castlevania or Metroid games, for me it is really the HollowMelee genera (I've played several others but all fairly recent games I think). I checked that Wikipedia described both of the first Metroid and Castlevania as platformers; I didn't know it was the later game that more distinctively defined the genera. I admit "what exactly qualifies as a platformer?" is also a hard question and I argue for a stricter definition so on further consideration I agree that "action" is the better category to use.

For 3D (in the sense of first person or close to first person), it does seem like I haven't ever played a 3D metroidvania. I first wrote "(are there any?)" but then did a quick search and saw a list that I don't think overlapped much with the ones you mention and included Supraland (which I have but only played the demo so far) and Batman: Arkham (I guess I didn't fully edit the comment). I have played a number of 3D platformers and they have such a distinctly different feel that I can't see how it is useful to consider them the exact same category as 2D platformers. Additionally, I often get nausea with 3D games, so for that reason as well it is really important to be able to look for only 2D games at times (racing games that have a semi-fixed first person perspective seem ok as well). I guess as long as there is a way to look for only 2D or only 3D games it doesn't really matter if it is considered a distinct category or not. Thinking in terms of the Ys games that I have played through the 3D transition, I guess I could see how someone playing the same series through the transition could consider them the same category, although I find them quite distinct. I don't dislike the 3D ones, they are just different.

VVVVVV is an interesting case, GOG tags it as metroidvania but I don't think it should quite count (everything can be explored from the beginning).

I found via Wikipedia an interesting translated interview with Koji Igarashi, assistant director of Symphony of the Night (and producer of most of the later Castlevania games and Bloodstained: Ritual of the Night). He said the main inspiration was not Metroid but rather Zelda and wanting to make the game longer since games were much more expensive than movies. His list of "Metroidvania Guidelines" (my summary):

1) Player control: the player spends the whole game controlling the character. "Controls are fun = game is fun".
2) Feeling of exploration but not free rein. Branches.
3) Enemy balancing. Make bosses the best they can be.

Only #2 is at all specific to metroidvanias, though, so it doesn't help much to define the category (every game developer should put "controls are fun = game is fun" on a poster). In response to a question he said he only heard of the "metroidvania" label in maybe 2012ish (but likes it and appreciates the connection with Metroid) and they called it "2D exploration action game" at the time. Matching what you said, he mentioned that they would have made it 3D but didn't feel like they had sufficient experience to pull it off and making it 2D let them use art from the older games.

Also, while I gave up fiddling with my ad blocker before unblocking the actual content, Wikipedia also pointed me at this where the description I could read says: “Metroidvania” doesn’t exist, and Jeremy Parish and Scott Sharkey made it all up. That’s how I approached this episode of our humble video podcast thing...

True, but genre mashups aren't really new. Pure platformers are more about evading enemies than fighting them. See Super Mario Brothers and similar games.
Good point, I didn't think of them because I didn't play them since I didn't own the consoles they released on.

The original Metroid is definitely a Metroidvania, even though that term hadn't been coined yet.

The original Castlevania, on the other hand, is not. The game is separated into levels with no backtracking possible, and there aren't any permanent power ups (you lose everything on death, and picking up a sub-weapon will cause you to lose the sub-weapon you had previously). Whip upgrades last until death, but usually it's not going to take much time to fully upgrade your whip after a death.

If you have trouble playing 3D games I understand why you don't know many of them.

So let me recommend you a few 2D ones beside Hollow Knight, Guacamelee and Bloodstained, which you already know, just in case you don't know these yet:

Ori and the Blind Forest: Definitive Edition
Dust: An Elysian Tail
Sundered: Eldritch Edition

I can highly recommend all three but I would even go so far to say the first two are must play if you even have a passing interest in the genre.

When it comes to 3D you better have a look at gameplay videos on YouTube first to check if they make you feel nauseous but if they don't you should play:

Darksiders Warmastered Edition
Darksiders II: Deathinitive Edition

All of the games are typically discounted quite high. Winter sale should be around in 1-2 weeks so you can pick them up for cheap if youi don't own them yet.

There's some exceptions to that, namely the very beginning (which must be played before you can explore, barring a glitch), the intermissions, and the final level.

To me, what makes VVVVVV not count as a Metroidvania is the lack of permanent upgrades that allow the player to explore new areas.

Thanks for the recommendations! I did play Dust:AET about 8 years ago, that or Guacamelee must have been the first metroidvania I played (got both in the same Humble Bundle). I recalled it being more linear and actiony but checked a playthrough and I think I must have just remembered the very beginning of the game.

I've had Ori on my wishlist for a long time but was put off by the save system so I never actually picked it up. But I will soon and it even has a reasonable regular price. Sundered I avoided since I really didn't like Jotun, but I'll try it on your recommendation.

I'd love to try a 3D metroidvania too. Unfortunately, I also have an issue with blood and checking PC Gaming Wiki it doesn't look like the Darksiders games have a no blood option :(. Lots of games I would otherwise get with that issue. I'll at least give Supraland a try when I can since I have it (looks like it was pulled from GOG by the developer :( ). The nausea seems to get worse for weeks at a time, although Unreal Engine games are the worst and usually cause some discomfort that I can manage after adjusting settings during better times.

Also, I noticed that one of the developers of Where Birds Go to Sleep runs hallownest.net that has a (nearly) full map of Hollow Knight that can be zoomed to in game size. Really neat to see how much there is to explore.

Thanks. Nintendo has so many nicely designed games. If only they would release them here :(.

I'm not sure if the original Metroid would qualify as "nicely designed". The game is very rough, with such issues as:
* Whenever you start, respawn after death, or load a save (via password for US release), you start with only 30 energy (the game's version of hit points). This means you need to farm energy pick-ups if you want to get back to full health (initially 99, but can go up to 699 IIRC), or leave an E-tank uncollected for later.
* When you go through a door, you lose control during the animation. This wouldn't be an issue, except for the fact that enemies can still move during this time, and can still hurt you.
* There's some spots in Norfair where you can fall into lava, which *slowly* (emphasis on *slowly*) drains your health, but are unable to get out of without bomb jumping, which is rather finicky in this game, and is really considered an advanced technique anyway. Hence, the player is required to either wait for a slow death, or press Up+A on controller 2 (which forces a game over).
* No automap. If you want a map, you have to draw it by hand. Couple that with re-used screens, and it is easy to get lost. (Worth noting that Zelda 1 does have an automap, and while Zelda 2 lacks one, it isn't as easy to get lost in that game, particularly since there's the overworld separating the individual areas.)
* You can't save except via game over. (This issue affects many other games of its time, including both Zeldas and the Castlevania games (though cartridge versions of Castlevania 1 don't even have the ability to save; that was only present on the Japanese FDS version).)

On the other hand, there is one interesting case of clever design; if you start a new game, then go right (as is standard for platformers of that era), you'll eventually be blocked by a passage too small for you to fit through. To pass, you need to go *left* at the start (rather novel for its time), and pick up the game's first permanent upgrade.

Super Metroid is where the series really started to feel well-designed.

That does sound rough :(. I found a detailed map and I see there is quite a bit of lava :/. And I see they didn't make you go too far to find out that you had to go left, sounds like a good introduction to the non-linear thing. It is a surprisingly complex map for that time.

Most of the time, it's possible to get out of the lava and back to solid ground.

There is, however, at least one spot where it isn't possible.