Metroidvania games.

https://store.steampowered.com/app/230700/LaMulana/
Also La-Mulana 2 has a good rating on steam but i dont play it.

cant believe no recommend Dandara
https://store.steampowered.com/app/612390/Dandara/
won it here and just finished it.

nothing super hard but it sure was fun flying around

if you want to try something different/with a spin:
https://store.steampowered.com/app/813630/Supraland/

I recommend it

EDIT: you can try the demo

I love the genre and many of its games. But absolutely nothing can compete with the Metroid series itself. I've been addicted since the SNES.

There's a free Hydra Castle Labyrinth (not on steam).

That is... games where you unlock stuff that give you access to new areas, right? Ok then, games that aren't mentioned in this thread yet:

Rabi-Ribi - a metroidvania RPG Platformer with a lot of boss fights that use Bullet Hell patterns. :D It's very very good! It's also probably very very not for everyone. Gets pretty tough at times. Probably the game with the most varied metroidvania mechanics I've ever played- you can play normally, collecting everything and unlocking new abilities as you go along oooor you can absolutely beat the entire game collecting 0% of all non-story critical items (this includes not taking any weapons; and, yes, there is an achievement for doing this), get to the bosses in almost any order (there is an achievement for getting to the most far-away boss from your starting location first; also they are scaled to your collected items so it's always balanced) or even speed-run it in under an hour. It's also very very cute! ^_^

Evoland 2.

World to the West - 4 characters with different skill and terrain traversal and puzzle solving options. By the end it's super fun to figure out how to get each one of them to every part of the map, since they all individually have to get to places rather than moving as one big mass like in most other games that have multiple different characters like that.

Shantae Series - surprised this hasn't been mentioned yet considering it's an entire series of very good metroidvania platformers.

Hell Yeah! Wrath of the Dead Rabbit - kinda minimalistic on the metroidvania elements but still a very fun (and hilariously ridiculous and stupid) little platformer.

Castlevania: Symphony of the Night
Unfortunately it was never released on PC

Khimera is pretty darn good for the price of "nothing"!

HUGE FAN. Castlevania: Symphony of the Night is probably either my favorite or second favorite game of all time. The recent-ish Bloodstained is pretty great. Blasphemous is fantastic if you like Metroidvanias and Soulsbornes. Salt and Sanctuary falls into a similar category as the previous, but way more Souls-like. La Mulana and the sequel are pretty good examples of the genre, as is Treasure Adventure World. In the 3D space, give Supraland and the modern Tomb Raider games a go.

i love metroidvanias.totally bookmarking that thread.
like others already said, i realy like exploring the map, getting new skills and unlocking even more.
im currently playing guacamelee 2 on hard trying to get alll achievements.
sadly im not a good enough player to do all the achievements for most other games as they are simply to hard for me.
i cant beat that Grimm King in Hollow knight... and im not even playing on hard.
Loved Iconoclast and Ori and the blind forest as well

would chasm be something for me?

I only like them when they are not too complicated. The two games that are in my mind now are: Insanely Twisted Shadow Planet & The Messenger.

Luv Em, Platform Games are the best. IMHO it's the best genre.

Though I hate the term, Metroidvania, because Metroid didn't start it and Castlevania didn't contribute much to it (also, it has all of one title and part of the other; Metrovania is a better name, but at least it's not the old standard, which was Castleroid), I do love the genre. I prefer to call them Platventures, because it rolls off the tongue a bit better than Sidescrolling Action-Adventure. My absolute favorites in no particular order, but separated by system are

GBA

• Castlevania: Harmony of Dissonance

NES

• Adventure Island 4
• Blaster Master
• Legacy of the Wizard (debatably counts)
• Ufouria/Hebereke

PC

• Cave Story
• Outland

SNES

• Demon's Crest
• Super Metroid

Wii

• Muramasa: The Demon Blade

There are tons of other good ones, but these are at the top of my list.

Some recommendations not yet mentioned (and some not mentioned enough)

-LA-MULANA. Its GENIUS. Not for the faint of heart.
hardcore, very. Charming even more. Did i mention genious? The jump tough is so oldschool some may dislike it by it alone

-Abyss Odyssey
very interesting, mixing rogue-lite with metroidvania, 3 characters, unique setting
AND SMASHBROS gameplay because why not

-Apotheon
Unique art and mechanics

-Capsized

-The desolate Hope
Its free i think? Also unique and it blends some rpg elements as well.
you're a freaking robo coffe-machine that becomes sentient in a madworld of living machines on a abandoned starship of sorts

-Dex
Cyberpunk and rpg elements, kinda deus ex lite in platform

-Odallus
Kinda is. Theres separate levels but you go back and forth on then as you unlock new stuff so you can explore it all and such.
Lovely oldschool vibes.

-MAGICIAN LOOTERS
THIS IS AWESOME. Seriously.
HIDDEM GEM
Just buy it this sale. No need to watch or read reviews, go on, click on buy. I will wait.

-Wonder boy
Highly recomend. The new one, Monster Boy, is right now in my cart

-Strider
Rarely i can't drop a game, completely consumed by it until i finish.
Even more rarely a game that i finsh twice. Or twice and half.
And just mentioning it makes me want to reinstall it. THIS IS AWESOME
STRIDER IS SO UNDERRATED. Go get it! Its addictive! Faster then any other one, and slick, and thumb numbing and...
Another must buy. Like Magicians and La Mulana too.

-Super Daryl
Weird one of the bunch, a indie kinda rough around the edges weird creature.
It has some artificial grinding and replayability, but once you get past the initial roughness it can be a good time killer. Theres a lot to do and explore, dozens of skills, unique setting and art.

-Pharaoh rebirth
Split level metroidvania.HIDDEN GEM. Its awesome.
A must in my opnion. ALso one of the few i couldn't drop until i finished.

metroidvanias are probably favorite genre. most of the really good ones have already been listed on here but if i had to only list the ones that have stood out the most to me...

hollow knight
large map, great story, great dlc, plenty of very difficult optional bosses to really test your skills. i imagine this would easily be on anyone's top metroidvania list.

la-mulana
this is a very, very difficult game. it's absolutely massive and has so much to do. also has a sequel, though i haven't played it i can assume it's also good by it's ratings and my love for the first game.

blasphemous
i didn't get nearly as many hours out of this compared to the other two games above, but i absolutely loved it nonetheless. i just really dig the art style and story. bought it on release day and had it at 100% within a day or two.

dead cells and rogue legacy
those are a bit different as they are rogue-likes with procedurally generated levels. in my opinion though, dead cells is a much better game with many more hours of replayability, though both are definitely worth buying.

bloodstained rotn
i haven't played this yet because of the price, but i wanted to mention it anyways as it's the one metroidvania i haven't played that i'm looking forward to the most.

Good to hear that Chasm is good.

I absolutely love Metroidvanias, ever since I played Symphony of the Night. My favorite is Ori and the Blind Forest, because of the way the powers truly transform the gameplay and the way you look at the environment from start to finish.

I really like starting them, but after playing for a while, I tend to 'get stuck' trying to find the parts of the map that are now open but weren't before, and then stop playing,
I think it's a problem somewhat inherent in the genre. I did finish the Metroid Prime games; if I recall, the map highlighted areas where you got stuck.

Ori and the Blind Forest and Seasons After Fall are absolutely gorgeous. Owlboy, Guacamelee and Shantae are also fun to play.

Super Metroid for SNES was mentioned before, but only once, so let's praise it more!

And now, for something not mentioned even once and rather unknown: https://store.steampowered.com/app/311190/Super_Panda_Adventures/ - great little gem.

I want to recommend an strange and forgotten one.

Eternal Daughter (from Derek Yu, creator of Spelunky and Aquaria)
Beautiful pixel art, nice story and gameplay.

https://www.derekyu.com/games.html

Direct link, it's freeware
https://www.derekyu.com/games/ed.zip

Some great games mentioned already
Adding:
The Swapper
And seconding
Strider

The Vagrant.

Going through my library, I think we all forgot about Sundered.

Not a bad one to add to the list.

Bloodstained is pretty good!