Classicvania has another very, very interesting mechanic that separates it from other platformers (I'd still call it platformer since it still emphasizes movement, even if it's slower). Actions are comitted: most platformers and metroidvanias, once you jump, you can still re-align how you land by pushing left or right while in the air. The classic metroidvanias forced you to commit to your movements, which is easily the most tangible difference from other platformers: once you jumped, your momentum could not be changed. It presents a fairly unique challenge to the old castlevanias that we don't see all too often, and while most fans of platformers would enjoy it, it more or less is 2d dark souls before dark souls got popular. The intentionally clunky design is great for those seeking a proper challenge or something different. Of course, not all the games with this feature are necessarily linear, either (2 and 3). SoTN was the one that ended up defining future castlevanias and metroidvanias as a whole, which is why Bloodstained is so revered.

Another interesting thing to note: one of the things that people like to bring up about SoTN in particular is the feature to sit in a chair. I didn't understand all the hype with stardew and terraria until i saw specifically why it was a big deal in SoTN. In particular, if you go to certain areas and sit, different things will happen, and it's almost an easter egg of sorts, which one would say adds realism, another would say "who cares?" but in particular it causes one (well 2) of your pets to do things they don't normally do (1 sings, and they both sit on your shoulder, iirc). Then, in one particular room, there is a few easter eggs derived from sitting in the chairs in the room (a confessional) with semi-random outcomes. This, once again, reflects what alot of open world games attempt to do by having characters able to do things that add nothing to gameplay, but seem absolutely reasonable for them to do (like actually using a chair, even though video game characters almost always have infinite leg power).

As for genre merging, i don't think that's necessarily a bad thing, but it's getting to the point where companies are doing it to fill checkboxes, rather than to come up with a cool idea. The difference between the former and the latter is whether or not you're blindly throwing certain features together.

Then you shouldn't have said "indeed" like you were repeating what I'm saying.

Yeah thanks for the condescension but open world is something different and has existed in 2D as well - see Pirates! or Star Control 2 for example.

Open-world games tend to be the antithesis of MV. Item/ability-gating is the opposite of openness.

Metroid Prime is a fairly good example of a "3D metroidvania" and it's very much not an open-world game.

Breath of the Wild is an open-world game and it achieved this by removing the vast majority of the item-gating that characterised Zelda games from aLttP onwards.

I would say such jumps are mainly a holdover from before SMB's popularity which the CV series stuck with for way too long just to stand out and be old school or hardcore like the Ghouls 'n Ghosts and Ninja Gaiden games.

On that note, they're also in Mega Man Legends 2 from 2000, hehe.

No, the anti-thesis would be a rail-shooter. Open world games do attempt to restrict movement (all games do, fundamentally to the concept of game) but some are far, far more restrictive than others. Open world games and metroidvanias both have the intent of allowing backtracking while eventually opening up the whole game.
Neither do i, as i had stated. However, it's worth pointing out that this is probably the first thing you'll notice when playing the earlier modes. So from his perspective, classic is Rhondo of Blood (which he did before SoTN), however he knows that some people are looking for something even older. I wouldn't really consider "classicvania" worth a separate genre from "platformer," tbh (just look at the pool we're dealing with vs the pool of differences). Meanwhile, i'd consider Castlevania 2's committal jumps an abberation, kind of like we always have a feature or two that are abberations for their genre. The games that people consider classic castlevanias happen to have the committal jump attribute, but i wouldn't state that it's worth defining a new genre over, but I also wouldn't add a genre for the other differences, as well. When someone tries to separate these games, they're most specifically looking for the delinearization.

Not sure on the case of Star Control 2, as i haven't touched it, but Pirates! is not that fundamentally different from a 3d counter-part. This is something worth noting about top-down games in 2d, that they do often transition really, really well to 3d. Another 2d game you might find getting called "Open World" would be The Legend of Zelda.

And the comments frequently spouted about Zelda 2 should be a huge red flag that player perspective is huge on these points. Do you know any topdown metroidvanias? Do you know any side-view open world games?

I disagree here. It's not an aberration in my point of view because committal jumps mean that you're giving more control to the player over one more action your character can do. This adds one more layer of complexity to a Classicvania/Platformer. Since these, in grand part, are based in movement too, you're giving the player more strategical control through mechanics, that may, or may not, be used in player's favour.

First Legend of Zelda should definitely be considered an 2D open world imo.
Open World games are about freedom of choice in how you travel a world.

That example is clear when you see Breath of the Wild, which abandons many characteristics that were loved by fans, but returns to the original in essence (well, kinda of.). The original freedom of how you will complete your objectives are back, while linearity is abandoned. A wise and venturous decision, since their past games were pretty much linear.

A Link to The Past is a great game. Completely different from the first. Cool thing, Nintendo is always trying something new with Zelda series. I don't think we should be mad when they change the focus of a game for experimentation (if it's at least well done, not something like Assassin's Creed, for example...).

I'm happy because all of Zelda games try something new in each title, which is incredible if you notice the number of games in the series already. They failed a lot in many games, agreed, but they tried new things, which is good. Gotta give them that.

By the way, I'm playing Sundered right now and it's really fun. The dread and isolation of Metroid is present in this one too, so I believe it's a good Metroidvania. Progression seems based through new abilities and exploration. Only downside I'd point is the "rpg stats tree" which seems big at first, but when you explore enough, you realize it's actually kinda easy to level them up fast.

I haven't played the original, but the remaster looks incredibly well done.

Thanks all. I find this discussion & list very useful

Rail shooter is a completely different genre. Within action adventures, open world and metroidvania are nearly opposite ends of a spectrum.

In an open world game you can, by definition, go pretty much anywhere from the beginning. The less ability/item-gating there is, the more open the game is. The more ability/item-gating there is, the less open it is.

Sure there might be stronger enemies in some parts of an open world game that make it difficult to go to certain areas early on, but on a basic level you can go anywhere. This is the opposite of Metroid Prime where your movement is tightly controlled and it's only once all abilities have been acquired that the entire map is available.
Haha, I didn't mean for my opinion of Breath of the Wild to spill through here - I mentioned it simply as an example of how something open worlds and item-gating are opposites. You can have a mixture of both, but to have more of one means less of the other.

Except that:
* The least open games are those where you have separate stages that you play in order. Classicvanias are an example of this.
* In some metroidvanias, item gating isn't as strict; there are many places you can go right away, but doing so requires advanced techniques or glitches, resulting in the map being quite open from the start (or at least early on).
* Even aside from that, there are still differences in game structure. For example, in Guacamelee and Dust: An Elysian Tail, new abilities tend to just allow you to get minor upgrades in earlier areas, and perhaps to continue on the linear path. (Well, Dust's Chapter 3 is a bit less linear, but that's just one part of the game, and there's only one ability you get there that's used to access the rest.)

The Metroid games can be interesting to look at:
* Metroid 1 is basically open world once you get bombs, which are only the second upgrade (if you skip the Long Beam, which doesn't add any movement options). Yes, some upgrades will help with exploration, but they're not actually needed. (In fact, if you get the Ice Beam, you can even use a glitch to skip the two major bosses.) So, this game could be classified as "open world" while being a metroidvania.
* Metroid 2 is linear; you go to each section of the game in order, kill the metroids, then move on to the next. There is never any upgrade, whether major or minor, that you can't get in the first visit to one of these areas.
* Super Metroid is somewhere in between. There's a clear order in which the game is intended to be played, but with the help of advanced techniques (many of which were put in the game intentionally), you can play the game out of order (though Reverse Boss Order runs do require a glitch to get through Maridia (not Lower Norfair!)).
* Metroid Fusion is linear: You have to go to your next objective and can't wander off. It's not until near the end of the game where you can explore, get minor upgrades you missed, and get minor upgrades you can't get before.
* Metroid Zero Mission is like Super Metroid, except that, instead of advanced techniques, there are secret paths that allow you to sequence break. Furthermore, the later part of the game (everything from Tourian onward, which is a much bigger portion of the game then in Metroid and Super Metroid because there's a huge area after Tourian) has to be done in order, and there's still a lot of minor upgrades that aren't available until the endgame.

(I'm not familiar with the 3D metroids or the 3DS one.)

*I would argue that stage based games lack the adventure part of action-adventure.
*Sequence breaking doesn't count unless it's intentionally included.
*The games you're mentioning here are just another step towards the linear end of the spectrum.

As for the Metroid games you mention, they all demonstrate the point I've been trying to make which is that open world and item gating are opposite philosophies and that to have more of one requires less of the other.
Metroid 1 has relatively little item-gating and is consequently more open.
Super Metroid has a lot more item gating and is consequently less open.

It is in both Super Metroid (the game gives you advanced techniques) and Metroid: Zero Mission.

Yes, I'm familiar with both. That is a degree of openness, but far from being what the term "open world" means (to me at least). It's a spectrum, and a fully open world game would have no item-gating. This was the point I was trying to make to kohlrak, who was stating an equivalence between open world games and metroidvanias (suggesting that they are 3D and 2D counterparts).