Sulphur Nimbus: Hel's Elixir, a $6 (currently) game on itch.io. It started from the idea of an MLP fangame, but early in development evolved into an original setting.

This is a 3D physics platformer adventure with an unhindered flying character. Your hippogriff, Sulphur Nimbus, is an aerial photographer aboard a cargo ship, which is passing a mysterious atoll on the way to their destination. The crew want you to get pictures of the island, which has a castle that's been abandoned for decades. Unfortunately, after flying over there, a nasty storm builds up and you get zapped by lightning. After a flashback tutorial on how to fly, you wake up on the island shores, your wing is injured, and you have to run to safety, finding out this place is dangerous... so dangerous a resident dogicorn (like a hippogriff, but it's half dog and half unicorn instead of half bird half pony) has to rescue you when a lovecraftian horror tries to take you down into presumably Hel. Waking up in a castle room, your wing is healed, and you can fly again.

Now the game begins. Clear the boss monsters and rout them out of this island, area by area. Break the curse that binds you to this island. Find out what happened here.

What's unique about Sulphur Nimbus is the movement. Running, fighting, and jumping has physics to it, allowing for some parkour stuff to be possible, like running up steep inclines and wall jumping. Flight is realistic. There are no arbitrary limitations, other than a regenerating "flap" stamina. If you can get enough speed to take off, and if there's enough room to maneuver, you can fly. Level designs include lots of caves and enclosed spaces, but also lots of open areas, so being able to fly is a requirement to get through it, while also a challenge. While the game is designed for kb and mouse controls, honestly, a gamepad works very well with this game and is preferred. It also is cross platform, as it is made in java, and includes Windows, Mac, and Linux. The source code is on sourceforge and allows you to build the whole game yourself if you are so inclined.

There's no other platforming adventure game that attempts this, and I have tried every "become birb" game out there. They all are either bird simulators or use flight as a fast travel, but not as a core gameplay mechanic like this.

Copy Kitty: https://store.steampowered.com/app/349250/Copy_Kitty/ has a demo

Fun elimination platformer. If you wish Kirby did more with the power mixing from Kirby 64, you'll probably like it.

MOTHERED

An immersive first-person horror adventure where you play the role of LIANA - a young girl who arrives home after major surgery and is met with a strange mannequin claiming to be her mother.

This is part of a trilogy which I highly recommend checking out. All three of these are great.

HyperRogue has 352 reviews. It is a rogue like that is played on a hyperbolic plane rather than a euclidian one.

If you're not familiar with hyperbolic geometry, don't be fooled by the videos. It has the illusion of looking like it is on a sphere in many of the videos. It's not! Also, you don't need to be some master of hyperbolic geometry to play. I don't really understand it but can still play the game well enough.

Essentially, imagine a hexagonal grid. Now, replace some of those hexagons with septagons (7 sided). The further away you get from a point there will be way more tiles in the hyperbolic grid than the euclidian.

The UI is pretty bad, the menus are pretty icky. Those are my only real complaints.

The game is charming. It has.a very retro feel to it. The music reminds me of something of hear from an old school point and click game or RuneScape. The graphics are minimal but charming.

The mechanics are easy enough. You get hit and you die. Most enemies die in one hit. There are no weapons or stats. It's more like chess in a way. The game will also not let you accidentally move somewhere you'd die, so, yes, very much like chess with checkmates.

Because the game is so simplistic you can get into a flow state where you quickly move and attack enemies. It's very satisfying to play.

Ara Fell

The whole things just a massive labor of love from a relatively small indy studio. At one point it was an RPG Maker game that was delightfully well polished in terms of story, art, and environment. After the devs got tired to rpg maker limitations, they ported the whole thing to Unity and re-released it as a free Enhanced Edition update. Childhood me played the shit out of GBA Harry Potter and the Prisoner of Azkaban and it very much scratches that JRPG itch.

Aw yeah! This is where my knowledge of absurdly good but extremely niche games comes in. I think I'll make multiple replies to this comment.

Chronosphere

Think enter the gungeon combined with superhot, but simplified a lot. It's a turn based bullet hell, and an excellent arcade game playable in the browser.

EDIT: I'd also like to take this oppurtunity to talk about flashpoint. Flashpoint is a massive archive of basically every flash game and animation, and you can even play them again.

However, in addition to flash projects, I also noticed that flashpoint also archives HTML/HTML5 games... but only a subset of them. Although flashpoint's primary purpose still is as a flash archive, it can also be used as a curated list of HTML5 games.

Here is a website that lets you search the flashpoint database

NandGame is a browser puzzle game, where you start of by building basic logic gates from relays and progress from there all the way trough processor design to compiling high-level languages. It does not hold your hand too much, but the invidual puzzles progress so incrementally, it feels almost magical how easily you learn to build computers and compilers.

Minecraft (do your worst)

Grand Theft Auto IV

It's a little known game from a small publisher originally located in Scotland.

The main premise is that you drive around a city as quickly as possible and go bowling with your cousin. Think Big Lebowski meets Driver. You can also play Pool and Darts in various locations around the town, and earn money doing small side jobs such as being a taxi driver or a paramedic.

Chained Together

Multiplayer platforming game where you're chained to up to three other people trying to escape Hell by climbing up, up, up. I've only played it 2 player, which was fun, and can only imagine how chaotic 4 player would be. Can be played solo, but I wouldn't recommend it.

EDIT: For once, I'm glad to see downvotes! Good to know it's gotten recognition.

If I am incorrect about downvotes being inconsequential account-wide, say so and it might be possible to work out a different system.

Wouldn't "upvote if you have never heard of it" accomplish the same thing?

I guess it would depend on people reading and following the instructions, instead of just upvoting games they like. Maybe that's a bit much to ask. :P

Cave Story+.

You are Quote, an amnesiac robot. The world appear to have gone to shit and you don't know why.

It's a 2D sidescroller, which if I told myself, I would find immediately boring, but the animation, controls and story combined as just so good. It's so good.

Hand of Fate

A deck construction game where the cards you choose to put in the deck are the challenges you will face on your run. You unlock more cards by completing challenges on the cards you have.

You can skip the first one and play the sequel, it's more polished.