Anyone who has played enough metroidvanias will know that they're not all the same. So, how do you like them?

How linear do you like them? On one hand, you have games like Metroid Fusion, which are extremely linear with no backtracking; Cave Story, if it counts as one, would also fit this category. On the other hand, you have situations like the original Metroid, where there is no order. You have games that are pretty much linear with backtracking allowed, like Unepic and Guacamelee!, and then there are games that subtly guide the player without forcing it, like Super Metroid and Hollow Knight (though, after a while, Hollow Knight becomes significantly less linear.)

Do you like having RPG-style elements, like leveling up and random loot drops? You see them in the Castlevania games that fit into this genre, as sell as in a few others, like Dust: An Elysian Tail and Timespinner. On the other hand, Metroid games, along with games like Guacamelee! and Hollow Knight, don't do this, instead giving you upgrades through exploration. (Random health/missile drops in Metroid don't count here, as they only refill a resource rather than providing a permanent upgrade, and they can't be stored for later.)

Do you prefer the player character's main attack to be ranged (like in Metroid) or melee (like in most non-Metroid examples)?

Do you prefer the game to be more combat focused (like most Castlevanias), or more platforming focused? In particular, would you prefer the hardest challenge to be a hard superboss or a hard platforming section?

Edit: Remembered another thing: How do you like the world to be structured? Do you prefer there to be a hub that you frequently pass through, or do you prefer worlds where you start on one end and eventually reach the other?

Edit 2: Regarding Hollow Knight, the order I came up with will take you as far as the Dream Nail, but at that point there doesn't seem to be a single obvious direction. (The game does indicate what you need to do next, but there are multiple places to get this done.) Super Metroid, on the other hand, ha a clear order that goes through the entire game (though advanced techniques allow you to deviate from it).

More adventure focused like Ori.

Spot on.

Metroid-likes are definitely my favorites. They allow you to focus on exploration without sucking you into combat all the time. Also, I like that equipment in such games is limited and used cleverly. More equipment looks like more RPG, which is not my forte.

Oh, and I definitely prefer bosses that are well designed rather than hardcore platforming. Tricky platforming is welcome, but hardcore platforming should be optional.

I like my metroidvanias to be insanely convoluted, infinitely procedurally generated, and to have terrible mixes of HD artwork clashing with 8bit artwork at all times.

So honestly, I pretty much like everything in the Valley Without Wind series.

Like Hollow Knight.

Not like Ori, with it's "seamless" cinematic or chase scenes.
Not like Alway's Legacy with it's upside down areas.
Not like Chasm with it's backstepping and ledge-grabbing.
Not like Batbarian with it's controller-style aiming or darkness.
Not like Feudal Alloy with it's stamina or non-sorting inventory.
Not like Catmaze with it's hard-to-judge-size-of platforms.
Not like Environmental Station Alpha's graphics being impossible to make out what's what.

Not a fan of 2d side scrollers anyway, less so when theres platforming involved (though i do love to build in Terraria), but then i got Guacamelee! when it was free from Humble and while i wasnt engrossed enough to play more than an hour or two, I did ultimately get someenjoyment out of it.

Be interested to see if this thread suggests anything i may enjoy more.

I could, of course, mention La-Mulana, which is basically a metroidvania with adventure-game style puzzles (and those puzzles are actually really difficult, sometimes *too* difficult; I hear the sequel's puzzles are a bit more manageable, but you still need to think).

(Personally, I'm not into these sorts of puzzles, but some people here, particularly those who enjoy old-school adventure games, might be.)

I used to love this genre so much. Super Metroid was one of my favorite games as a kid, and despite being almost exclusively a PC guy I played the crap out of Symphony of the Night. All the modern indie ones though, I just bounce off them for some reason. I stopped buying them because I never played them for more than a couple hours, I guess I've just grown apart from that entire style of game.

I do love this type of design in 3D games and genres though, like Dead Space for example.

I'm not the most seasoned metroivania player, I've finished a few titles but separating aspects of the games is not my cup of tea, it's like saying I like McDonalds cheeseburger because it has cheese. I don't really like unskippable cut scenes but done right may be a non-issue.
For me, all of the OP questions depend on the game itself. and how those features are implemented.
That said:

One of my all time favorite title is Ori and the blind forest (I've played the Definitive Edition wich has fast travel), it's not a perfect game but many aspects are very, very good. I understand many people don't like the chase scenes but I've enjoyed the challange way more than the exploration itself. The music is superb (don't know enough to fully appreciate the technical side) and mix very well with diferent sections of the game.
For those who don't know the game it's more platform focused with little combat, the "bosses" are mainly timed hard platforming sections, very well done and quite satisfying, the music helps here.

Hollow Knight set the "good game" bar very high and I mean most genres, you have to learn the game to enjoy it.
For me, the combat/platforming combination it's the game highlight, It has a short melee combat/platform system that is very simple, yet can be more satisfying than many hard-to-hit combos on fighting games (the reduced competitive pressure may be a factor here). The game frequently breaks your rithm so you have to adapt.
The only issue I have with the game (save points "far"from bosses are mostly a non issue), is the replay value, wich funny enough is also one of the game strenghts. What I mean is that in the first playthrough, every thing is a big challenge and you learn and master techniques during the gameplay, however, after you beat one section, it turns considerable easier, meaning after beating the game, even the final boss is not a big challange anymore.
It's by far, the most all-round polished game I ever played and has virtually no downsides (before you quote me to argue, please finish the game. I didn't like it in the first 4-6 hours)

I don't have strong preferences in that I avoid certain series besides maybe the rogue hybrids, but I appreciate games that do these things:
-Seamlessly interconnected game world with some degree of persistency, more than one entry point for most areas and nice transitions between areas
-Some non-linearity in the overaching structure with subtle guiding in the right direction
-Movement ability focus and multi-purpose abilities/tools
-A sense of loneliness, vulnerability, and/or dread throughout most or some points of the game
-Environmental storytelling over narrated/character-driven
-Good sequence breaking opportunities
-The world changes as you return to previous areas, with new paths, new ways to travel or new enemies, or all three. I also like major environmental changes like in Arkham Asylum for example (poison ivy, just the first game I thought of atm).
-Some kind of fast travel
-Good puzzles
-Concise world and content design, not a lot of dead space and soon to be useless gear

I run a site about retro MVs since a couple of years back, so I play a lot of them. Some faves:
Super Metroid, AM2R, Metroid Fusion, Metroid: Zero Mission
Wonder Boy 3 and Monster Boy
Gargoyle's Quest series
Ori 1
Castlevania: Circle of the Moon, Castlevania: Symphony of the Night, Aria of Sorrow
Dragon's Curse Remake (fan remake from 2008)
Ufouria: The Saga/Hebereke
Metroid Prime
Guacamelee
System Shock
Aquaria - Just barely as it's a bit rough in some ways and has a slow start, but is also fairly unique, has a great map system and is pretty open-ended, more so if you count sequence breaking

MV-lite:
Front Mission: Gun Hazard
Quackshot
DuckTales 2
Land of Illusion Starring Mickey Mouse
Flashback: The Quest for Identity
Spyro 2
Exhumed

La-Mulana I played through pretty recently (2005 ver.) and enjoyed certain aspects of, but loathed others. It's too stuck in the 80s in various ways and basically requires a guide or asking people who've played it to get anywhere within a reasonable amount of time. The platforming and combat challenge wasn't too bad though, and it does have a rather forgiving fast travel system.

Hollow Knight is quite good for the most part, just didn't care for the boss focus and overly high trial & error-based challenge (I did get the good ending) with backtracking to bosses, certain aspects of the map system, or the heal mechanic, or the ricochet when hitting things, and some other quirks like the audiovisual effects during combat. I've considered replaying it but when I start thinking about all those things I just don't feel like it.

Worth noting: Monster Boy and the Cursed Kingdom has a lot of race and chase sequences.

I think Castlevania Symphony of the Night and Bloodstained are my favorites.

I did play all classic Metroid games (1, 2, 3, Fusion and Zero Mission) and that Metroid 2 remake AM2R. I enjoy them very much, but I haven't tried the more recent versions.

I also played all GBA Castlevanias and liked them as well.

I played Castlevania: Lords of Shadow – Mirror of Fate, Hollow Knight and Chasm as well. They were nice and fun, I liked my time with them very much, but I didn't fall in love with them.

Shadow Complex irritated me until I dropped it, but later I got back to it and finished it.

Overall, I tend to like random exploration and becoming excessively overpowered in these kinds of games, and hate elaborate, complex battles/battle systems. If a game is aiming at being 2D Dark Souls, I probably won't like it much, and certainly won't love it.

Save points far from bosses is an issue, as it makes such bosses more frustrating and makes it more of a pain to learn the fights. It's also part of my biggest issue with the game, that it punishes failure too hard. Honestly, the game would have been better if it had a mode where you don't have to find a shade to get your money back and fix your soul when you die, perhaps also with an option to restart from the start of the room when you die (a feature apparently present in Alwa's Awakening/Legacy).

If you find the final boss to not be a big challenge anymore, try going to Godhome and doing the following:
* Beat the Pantheon of Hollownest. (If that's too easy, you can add bindings to make it harder.)
* Once you've reached the final boss of that pantheon, you can fight them in the Hall of the Gods. Can you win that fight on Radiant difficulty (you die in one hit)?

On any case, coming from Celeste, there's a stark contrast in the way difficulty is handled in Celeste vs. Hollow Knight. A typical player is going to die far more often in Celeste than in Hollow Knight, but Celeste doesn't feel as frustrating simply because the penalty for death is nearly 0; you get sent back to the start of the room, your death counter increases by 1, and you can immediately try again, learning the room until you can clear it. Hollow Knight isn't so nice in this respect.

(With that said, note that Celeste is not a metroidvania; it's a precision platformer (that reaches kaizo levels in its postgame content), there's only local exploration, and there are no collectible power ups.)

Have you played Timespinner? It's very much in the style of the Igavianias, so if you like those Castlevanias, you'll probably enjoy Timespinner.

IMHO both a non issue, because the path to boss is usually extremely fast (there are a couple of exceptions, notably the boss I die the most times Traitor Lord), you eventually get teleport and you dont need to go find the shade, that's whats Jiji is there for. All challenging games are frustrating one way or another.
I'm very close to 112% complete the game, haven't play it for a month due time constrains, however the last Pantheon and Path of Pain are not only challenging but near impossible for us mere mortals with limited time and reflexes. That said if you re-read my post, my point was the replay value, not the dificulty.
Keep in mind the GodMaster DLC, wich includes all the said absurd challenges, was launched later because of the poor replay values.

Agree that Celeste is not comparable to Hollow Kinght (disclaimer, I only play Celeste for a couple of hours), it may be more Ori style.

I have it on my radar, but haven't played it yet.

Another I just recalled, that I enjoyed, though more linear, is Shantae and the Pirate's Curse. Very fun game, though the last level and boss are bullshit. I'm yet to try the other Shantae games.