It's written in Brainfuck, but it's really really good. Trust me, bro!

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.

>There's plenty of moments in hollow night where it can be way more than just 3 screens Name them. I'd be happy to counter.

Hey, hi everyone. We here at IronRaven decided to make a metroidvania, in the style of Dieselpunk and the 20s, art deco, art nouveau and so on. Tell me, what is the most important thing for you in metroidvanias, besides their appearance?

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

Take it a step further: include an option to disable all cutscenes and a speedrunning mode with in game timer.

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.

Please, playtest with unexperienced players

Absolutely this. If we're going to take a Metroidvania as an example of this lesson, let's take Environmental Station Alpha. The game has a ton of potential as a good Metroidvania that is buried in a thick armor of speedrunner-level difficulty. I have never seen a Metroidvania be so stingy about health tanks, and this game desperately needs all of the health tanks you can get. It stinks of a developer team playtesting the hell out of their own game, and making difficulty decisions based on years of their own self-testing experience. When you release a game with a Normal difficulty, no Hard difficulty, and then are forced to create a Easy difficulty *after release*, you know you've fucked up. Here's how you do it: You can playtest your own game, but that one gets the "Hard" label. If you playtest for a Normal difficulty and you can't imagine how to create a Hard difficulty, the difficulty range is completely off. And Hard doesn't mean "only people in the double-digits can beat it". That's not even a scale, or just reserve that for some "Impossible" difficulty, if you want to get to 5-6 levels, like Doom does. Normal should be some reasonable setting based on how others playtest the game. Get some expectations from your playtest audience in terms of the kinds of games they've played and beat before. Are they complete noobs to any sort of fast-paced gameplay, or have they beaten other Metroidvanias or games like Cuphead? Based on that, figure out whether the advice they give you applies to an Easy or Normal difficulty curve.

Counter to this: Don't cater to noobs. Hollow Knight is one of the GOATs because it's hard, but *extremely* fair. Learn the patterns, and any boss can be beaten hitless; explore properly, and any boss can be returned to rematch -- after a death -- from a bench in 1 to 2 screens (late game even has a teleport ability!).

I mean it happened to me a few times when exploring. I don't know the names of the places. It was still kinda early on. I think the messy place I tried to enter was the mushroom place? And i kept dying in there then had to travel what felt like half of a full zone to get back there because i had yet to find a bench in there.

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.