Return of the Obra Dinn is a great and very unique game in my opinion. A fun investigation game that makes me feel smart for solving it. I wish I could replay it, but once you've solved how everyone has died aboard the Obra Dinn, there's not much reason to replay.

Sexy Brutale

Space Station 14!

There's no other game like it. It's so absurdly in depth! You can play super hardcore with loads of knowledge and be next to a total casual in the same shift both enjoying your time together!

It's in early access on Steam right now. Ask and you shall receive!

https://store.steampowered.com/app/420840/BLARP/

BLARP! I suppose it's a physics game but I'm not aware of anything else quite like it. It's incredibly simple, addictive, and could only really exist as a VR game.

Shout out to Superhot and Noita, already mentioned in this thread.

Outer Wilds

If you're a naturally curious person, the odds are you will probably enjoy Outer Wilds. No other game I've played has ever had quite the same blend of mystery, conquering the unknown, and semi-realistic space exploration.

Could someone make another game like it? Not impossible, I suppose, but I think you would be hard pressed.

Should you keep playing the original? You really can't, one time through is all you get. Once you have discovered all the secrets and uncovered the mysteries, that is your journey through it. Still fun to visit every once in a while, though

I've got a couple games that maybe fit this category.

• Kerbal Space Program. This had a sequel coming out that apparently wasn't going very well and was cancelled, so right now, the possibility of a complete additional game isn't that great. Spaceflight simulator, where one can design and craft spacecraft and amospheric craft, as well as space bases. One can fly to other planets, set up bases, set up satellite networks, etc. There are some "build your own vehicle"-type games, but not as much of a hard sim as this. I believe that X-Plane can handle atmospheric craft modeling, though the scope of that game is much smaller and it focuses more on flying the aircraft. Has a campaign to progress through, where one performs discoveries and conducts research. I'd recommend this to someone who hasn't played it and likes sim games.

• Kenshi. There's a sequel coming out, so maybe it won't be unique at some point. They player controls a squad that moves around the world in real-time -- there isn't an "overworld map". The squad can be split up into multiple squads. One can build outposts and defenses and such and have something of an automated economy. There's a tech tree. The world has various factions and dynamic control of regions, something like Mount & Blade: Warband. There are unique biomes to travel through. A fair bit of the world is placed. The world starts out in a mostly-hand-crafted, fixed state, but evolves over time. Character progression isn't based on point allocation, but on specific experience; have a character get hurt, and over time his ability to take damage will rise, and so forth. I think that this is still worth playing, though it's by no means a beautiful game and possibly (hopefully) will be surpassed by its sequel.

• Majesty: The Fantasy Kingdom Sim. A real-time colony sim that can mostly run itself. One has indirect control for the most part; one directly controls upgrades, certain spell and structure abilities, and can spend money to create "incentive flags" to create missions for characters to fulfill. I don't know if it's right to call it a single-game genre -- it's a colony sim, and other colony sims exist, like Rimworld, Dwarf Fortress, and such. Populus and some god games have direct control over spells. But I don't know of any other colony sim that plays much like it -- most of the focus is on upgrades and on countering waves of invaders, and the gold economy is ununusual. The same developer tried making a sequel, but eliminated the "sandbox" mode, and turned it into more of a puzzle game, and that game didn't do very well. One builds a colony in real time. There is no direct control over the individual characters, but for certain actions, one can spend money to incentivize them to do certain things. Characters level up and purchase equipment using gold they earn and that you expend on them to purchase items. Some of your control comes from things like building inns to cause them to spend idle time in particular locations. Building construction and maintenance is carried out automatically by peasants. As adventurers spend gold at buildings, it comes back to your control. I think that I'd have a hard time recommending today due to its age (you're going to have 2d pixel graphics that are going to be tiny on a current computer).

• Pinball Construction Set. This is a video pinball game where the player can use premade elements to easily put together their own pinball board. Very elderly now, dates back to the early 1980s. I remember being absolutely fascinated by this back in the day. Since that time, there have been many video pinball games, as well as some systems that permit some level of authoring capability (e.g. Visual Pinball can run user-created pinball boards), but these require a lot more effort and expertise and "real" authoring tools to put together a pinball board; one can't just drop in in-game and start throwing elements together. I don't think that I can recommend this, as it's absolutely ancient today.

• Noita. It's based on Liero, but really not at all like it. It's an action-roguelite (well, that's a genre, but nothing really similar beneath that level of specificity) that has side-scrolling over an open world. Various materials interact and have their interactions simulated at a per-pixel level, something like the "falling sand" genre. However, there are enemies running around, and the player controls a character that walks and floats through the world. One can find various containers of substances; one can try and mix things together to manipulate the world. One finds wands with spells; one can combine spells and various spell modifiers on wands to create all sorts of custom magic weapons that can range from utility to offensive. The aim, as with many many roguelites, is to try to use some luck and synergies between various items to come up with truly game-breaking combinations. I can definitely recommend this game; I found it to be very good value-for-money.

Honorable mention:

• Hostile Waters: Antaeus Rising. This is not a single-game genre, but there have only been two successful games in the genre, and one, Carrier Command, is from the 1980s (and which I've never played). You control a carrier (strictly speaking, an amphibious assault ship) that moves along an island chain; it can create surface, amphibious, land, and aircraft and weapons for these. One has a limited number of AIs that can control some vehicles automatically; one can give general orders to these, control the vehicles directly. One can capture more resources from the islands to expand one's abilities. There was a remake of Carrier Command, which flopped, and a sequel, Carrier Command 2, a relatively-recent game, but unlike Hostile Waters, is really intended to be played cooperative multiplayer; playing single-player places a very heavy workload on the player...so I have a hard time placing it in the same genre, even if it has many similarities and was inspired by the same game. While I enjoyed Hostile Waters and I think that it could still be enjoyed, it's getting a bit long-in-the-tooth graphically, and I recall it being a bit unstable even back in the day.

Psuedoregalia

Basically Mario 64 mixed with a metroidvania with awesome vibes. Never played anything else like it.

The Stanley Parable doesn't really have a genre, and I don't think you make another entry into that genre without being derivative. There's a couple games I can think of that have themes of player agency, Bioshock and to a lesser extent Spec Ops: The Line. Just some ramblings.

While it's a series, it's really the only franchise like it, so it kinda is its own genre: Katamari.

Hardspace shipbreaker. You are a wage slave in orbit, disassembling and salvaging ships and binning the components. It's very dystopian. Essentially it's a puzzle game, to maximize profit and completion rate, but with physics and lasers.

Pyre. Guess where my username comes from.

It's a supergiant game so the usual is there: Great characters, interesting story, great dialog, fantastic art... very touching and inspirational all around. To this day it is the only game that has actually made me feel conflicted about playing well.

At a certain point in the story I just couldn't, and it felt like my hands were sabotaging my game independently. Weird ass feeling. And purely for character reasons, nothing really to gain from it mechanically.

What I love about it was that this wasn't really presented as a typical videogame dilemma. Nothing in the gameplay was different. It was just another "game" that I was expected to win, but one of my characters was desperately hoping to lose.

Well I lost that time and felt good about it. No game has made me make a decision that completely ignored the gameplay implications.

"Do you want to save this little girl or literally torture her and suck her life force? The evil option will give you immediate rewards but the good option will give you better rewards a little later and also the good ending!" Wow Bioshock, really tough choice there, thanks for putting my noodle to work.

EVE Online AKA Spreadsheets Online, back when I played it in 2009. No idea if it's the same now. Almost entirely player driven economy and factions (outside of hi-sec).

Elite Dangerous, sort of. No other Space Sim is on its scale (I wouldn't really call something like Space Engine a space sim). Unique, but mixed recommendations because it's a very shallow game in a lot of ways, but it's got a cool vibe. Speaking of which...

Space Engine. Not really a game, so much as a universe-simulator. It is unknown to this day how a mortal could create something of this grandeur. Maybe the source code will be released eventually.

Someone else already mentioned Noita :(

Cataclysm: Dark Days Ahead is the most realistic game ever made. No other game had made me ask "what would I do in real life?" before. Of course, this dies out the more you learn the meta, but your first dozen or so runs are special.

Minecraft is hardly unique now, but when it came out it was one-of-a-kind.

Death Stranding. One of my top games of all time. Atmosphere, gameplay, music, Kojima wackiness. It’s loosely in the “transportation” category of games, but it’s not quite a trucking sim, not quite a walking sim, it is story driven, it’s at least half survival-horror, there’s some stealth-action in there. It’s single player and also kinda multiplayer. We laughed at Kojima when he called it a “strand-type game” but it really is a wholly unique experience. The absolute closest you can come to another game like it is Snowrunner, but that isn’t story driven, you never leave your trucks, there are no enemies, etc.

Diary of a Spaceport Janitor is a slice of life/poverty simulator in which you scrape by earning pennies, dreaming of escape and adventure. Full of charm!

Miasmata is a horror/cartography game where you have to triangulate PoIs in order to fill out your map as you search for a cure to your disease on an uninhibited tropical island.

Yoku's Island Express is a metroidvania/pinball game in which you traverse the world vis flippers, chutes, and as a bug rolling a ball.

Pacific Drive is weird but really fun. It's like DiRT meets CONTROL.

I don't think it needs another. It stands alone as a testament to an interesting game design that shouldn't be watered down.

I have yet to find another game that plays like Inscryption. It's a deck builder, but wow, it has a story. Interestingly good game that I want more of.

While Elite Dangerous is part of a genre, it is a rare game that is actually meant for lots of controller/J HOTAS methods and has shockingly deep gameplay. You can tell it was really meant for adept players, a rare style of games these days. I doubt we will see one like it for awhile, just due to the needs of consumers, the game engine, and the capital required to build a game of that size again.

Gods Will Be Watching is the one that comes to mind for me. It's a strategy game of sorts with about 7 or 8 totally different scenarios where you're managing a very bad situation. In one, you're holding hostages while executing a heist, and in another you're wandering through a desert with limited resources. Each one is a balancing act, and a through line forms the narrative across them all. It was probably hamstrung by its punishing difficulty at launch, which was later addressed by additional difficulty modes, but there's a lot of room to iterate on this concept without it ever getting old.

"Giants: Citizen Kabuto"

It was a hillarious mix of everything. Super funny characters/story, great telling, fps, rts, asymetrical... All being super casual. Still on gog and still a joy.

"battlezone"

Best blend of rpg/rts/Story. So far i never saw one coming close that gameplay.

Maybe SimEarth.

This simulates a tile-based planet map. Animals grow and evolve, and things like atmospheric concentration and other aspects like surface albedo can be altered. More a toy than a game. Had a lot of fun playing with the levers.

1990 release -- it's still playable, though it'd feel pretty ancient and will not be very beautiful.

I haven't played SimLife or Spore, and there might be some similarities there.

I'm not aware of anything else that'd be comparable.

EDIT: Liquid War. This is open-source and part of the GNU project. One has a map with some areas closed off and some open space that liquid can flow through. There are two or more "blobs" of liquid of different color; each is attempting to destroy the other. Your blob is attracted to your mouse cursor. "Moving into" a pixel of the other color eventually converts it to your own. If two liquids meet in a bottleneck, they tend to stalemate. One wins by getting liquid on multiple sides of the opponent's liquid, so that one can move one's own liquid from multiple directions into it. Maybe a bit closer to a tech demo than a full-on game. I wouldn't call it mind-blowing, but it is free and as far as I know unique, and I had fun with it.

Terra Nil. It's an anti city builder. Land in a polluted wasteland, clean the soil, plant seeds, set up ecosystems, make sure they can persist without you, and recycle all your structures before you leave. Appreciate the beauty of the natural ecosystem you restored as you fly away.

I want more games like this.

Is it fair to mention Undertale? It's kind of an anti-RPG.

I recently got hooked on Twinkle Star Sprites, a Neo Geo versus shmup. Chaining enemies on your screen sends attacks to the opponent's screen. Those attacks can be bounced back, and reversing a reversal can create special attacks or even a boss summon. There's a lot going on and it's tragic that no spiritual successor ever tried to recreate this formula.

It did get a JP-only PS2 sequel, but it looks to just be largely the same game, just with a different cast of characters and the lovely spritework replaced with a much worse low poly 3D.

Frog Fractions
Universal Paperclips
Freedom Force
Pilotwings 64

Team Buddies for the ps1. Small team rts game, lots of unique units and the bright style is a great contrast to the fighting