Then it would be a game I never touch; when there's no other way to learn than by dying, your game has failed in my opinion. I shouldn't have to beat my head against some pattern that I can't discover through lore or elsewhere in the game. I'm in my 40s and used to game competitively in the early 2000s, FWIW.

Aside from the obvious things mentioned about flow, maps, immersion, etc., and to address some of the other things I've seen in the comments: configurability. Realize that not everyone will have the same physical abilities, skill, and/or time to play. Give options to people who want to tweak things to be more difficult and likewise for those who want it easier and more accessible.

Secrets. Secrets everywhere.

But also, be sure to eventually post about them *somewhere*. Don’t do the whole “devs left this secret in the game that was so obscure and difficult to find that it wasn’t discovered for 20 years” BS.

That Prince of Persia Metroidvania that came out a couple years ago had a very useful feature where you can not only make custom marks on your map, it also attaches a screenshot to the marker that pops up when you hover over it. Super useful, and I'm not sure I've ever seen it used in other Metroidvania games..

If it's going to have some kind of inventory system... figure out a way to prevent players from hoarding high-value items until the end of the game, at which point they are either meaningless because you're so leveled up, or else you can trivially defeat the final boss by spamming all the holy hand grenades you've been socking away.

Flow. Don't interrupt me. The rest of this just is about it in various aspects. Make it feel good to move from the get go. Don't make progression about getting rid of negative traits. Combat as well. There's a trend of making the player halt their progress to handle an enemy in a certain way (e.g. gotta wait for the telegraphed shield drop) and that makes backtracking and exploration tedious. It can be challenging going through the first time, but don't interrupt me with the same thing over and over. Let me ignore the puzzle/timing element by being overpowered or at least let me bypass it with increased mobility. I prefer bosses (and terrain) that can be overcome with skill or preparation. Like if you book it to them with minimal exploration they're hard but not impossible, but if you explore everywhere you can and find everything it should be easier. Don't artificially keep the player's abilities capped to make things more difficult. Also, no invincibility phases, please. I dislike items that only provide access like key cards. Every item that opens up more map should be useful in some other way. If there's a plot that is more complicated than can be explained in two sentences (Find the Metroid. Kill Dracula.), please make it good. Have non-cliche characters, plots that I can't immediately poke holes in, plot that isn't contained in logs that real people would never keep, and reasonable time frames for world changing events to occur. Those things all rip my suspension of disbelief to shreds. Don't make me sit through world building info dumps. Let me skip scenes and tutorials in case it's my second time through.

leave out the unskippable cut scenes... lookin' at you, metroid fusion.

Appearance, story, setting, and style are all mostly secondary to the mechanics and design of the game. Strip away the appearance of metroidvanias and you have a platforming maze with gated areas unlocked through progression. The overall maze of the game should ideally be enough to get lost in. Whether the world is going to be procedurally generated or predesigned, or some combination should be figured out early on. Even if progression is linear the access to and pathway through the maze should likely not be a straight line. It is very common to see or view inaccessible late game areas in the early game, for example. The gates of the game traditionally come in the form of new movement options. The reliables are usually: (double) jumping, running, slide/rolling, climbing, swimming/sinking, flying/gliding and so on. Choosing how and where the player may access these is important. This is to say: player movement is the game. Another common 'key' to gates is something that allows the player to defeat an enemy or boss they could not previously defeat, or otherwise access a new area. A notable example being metroid's ice beam. Freezing enemies gives the player new platforming options: and new movement in the game. Good new metroidvanias are aware of what has been done before and try to innovate on those tropes.

But also, don’t fucking do what Metroid Dread did, and try to defeat sequence breaks. The Dread devs went out of their way to ruin speed runners’ experiences, by basically fighting against sequence breaks at every opportunity. Sequence breaks aren’t something the average player should be able to do accidentally, but don’t try to actively stop it either. Maybe someone discovers that a particular platform normally requires a double jump to reach, but can be reached by kiting an enemy across the room and using some well-timed damage knockback to get a boost in height. This obviously isn’t intended gameplay, but it may be something that speed runners learn to do reliably, because getting the double jump ability adds 10 minutes to their route. *Don’t fucking patch that out as soon as you learn about it*, because you’ll just stifle any interest that speed runners have in your game. And in a decade, there’s a very good chance that the *only* people keeping your game relevant will be speed runners.

Well, it's part of the gameplay that you have to come back to. The benches are an important part of the difficulty, just like permanent death is part of the genre.

Thanks for your opinion! I found this mechanic weird and overdone in Prince, but I'll think about it since people find it convenient

Call me old fashioned, but I prefer specialized engines over the current trend of engines being made to do almost anything out of the box. Also D is not like Brainfuck, but C if it was designed well (and had optional memory safety).

Too many metroidvanias have abilities that work more like keys - they open a door that gives access to a new area of the game. A better ability is something that changes how the game fundementally plays, or makes old areas feel fresh. Starting the game with sufficient movement is a big one. Hollow Knight starts with too few movement abilities, and the beginning is slow.

Isn't "abilities unlock areas" like... The whole point of the "metroid-" part? I'm honestly asking about your opinion. I don't think there's a... concrete definition?