I don't think it's fair to call it a cult classic just yet since the game is rather recent, but eventually i think Kenshi. It's a really fun game although very grindy and i'm not even sure which genre it belongs to. Also it's very moddable to fit even more to your preferences. It's been quite a while since i played it, but i'll share a little story: I started the game for the first time and i wanted to make a "waifu squad" consisting of only women so i did. Worked my ass of mining copper and selling it in order to hire more ladies. Eventually my two ladies started to build a base near where i was mining copper and then one day, the "prayer day" (or whatever it was called) came and an army of crusaders came to spread the word of god. The bishop asked my main lady if there was any men in this settlement and of course i answered no there is none. To them it was blasphemy to not have any men in a settlement and the army slaughter my two ladies like it was nothing. Too bad i lost this save since i've gotten a new PC because i would've wanted to go on with my vengeance story, but maybe i'll fire it up again.

The Age of Empires series, especially AOE2. There's a nice digitally remastered version on Steam and I think it really holds up.

Wololo!

Beyond Good and Evil.

Dungeon Keeper, Red Alert 2, Unreal Tournament.

If you like Katamari Damacy you should try ps1 game called “Incredible Crisis”.

It is an extreme wacky minigame… game, one of those games that is simultaneously addictive and punishingly difficult. You play as four members of a japanese family trying to get home for grandma’s birthday, and insanity ensues. (Aliens, bank robbers, etc).

It got an english release back in 1999 but I dont think it made a huge mark. In any case, its very fun and ridiculous. Especially good to play with friends. It also has an amazing ska soundtrack by Tokyo Ska Paradise Orchestra if you enjoy ska, haha

Black and White.

Prince of Persia: Sands of Time.

Jade Empire.

Sphinx and the Cursed Mummy.

Sid Meier’s Pirates.

I don't know if Gothic 1 and 2 qualify as true cult classics or not, but clunky controls and interface aside, these are two of the best games I have played in my life. Gothic 2 especially. The games offer an atmosphere like nothing I've ever played. The soundtrack, themes, and overall color pallete provide this rich and stirring ambience that always manages to make me feel as though I'm exploring an ancient pine forest on a dark, rainy day. See for yourself.

https://youtu.be/HZ1tyNFODM4

You can feel the spirit of the entire franchise contained within the first two minutes of that audio track, perfectly encapsulated. It was an entire world apart and years ahead of its time. If it resonates with you, then these games are absolutely worth the initial difficulty of figuring out those ridiculous keyboard controls. But if you're really struggling with them, just read up on the Gothic 1 storyline and then skip straight to Gothic 2. It picks up right where the first leaves off. You won't miss a tremendous amount, and the controls and gameplay are infinitely improved. However, sticking G1 out long enough to figure out what you're doing will make G2 far more rewarding when you reunite with various characters and revisit previously explored areas.

A studio is remaking Gothic 1, but everything I've seen of it so far is about as faithful to Gothic 1 as The Dark Tower movie was to the books. They've massacred it. So stick with the originals.

Nox (the better single player Diablo, with some incredible game mechanics, even looking at it today)

Hexplore

Imperium Galactica

Giants (this game ran like shit on every age appropriate PC, I'm kind of wondering if the engine can even run without stuttering, but it's a fantastic game)

Gothic 1 (alive open worlds are not that new and exciting anymore, but this game has a lot of charm & an amazing sense of exploration)

The Longest Journey

Knights and Merchants (combat strategy game, the later levels are combat only and it's very HARD)

Rage of Mages 2

Chrono Cross (probably the best jrpg of all time, but the combat system scared away many)

These are not really forgotten & qualify for being a cult classic, but merely they are old titles that the new kids have never touched:

Baldur's Gate 1-2

Morrowind (so much better than Skyrim, it's not even close)

Pharaoh & Caesar 3 (the city builders, there is a recently released HD remake for Pharaoh)

Oddworld: Abe's Odessey (Much better art style & direction than in the still great remake called New and Tasty)

Jazz Jackrabbit 1 (Sonic feels soulless compared to this)

Settlers 3

Chrono Trigger (It's not really a cult classic, because eventually all jrpg fans play this, right, RIGHT?)

Im not sure how forgotten it is but Riven: the sequal to Myst. I always thought Riven was way better yhen Myst. I rememb3r being sucked into the world when i was a kid. It was world building and such a beautiful and unique design. I played it again a couple years ago and still holds up.

Stronghold, the castle simulator with a lot of charm but a dev team that lost their touch after a few sequel attempts.

Giants: Citizen Kabuto

Maybe Shenmue and maybe Unreal Tournament 2004 :D

Vampire: the Masquerade - Bloodlines. Dated, needs mods to run, but the fact that there's still a community patch being made for it after all this time says a lot. Haven't really heard much about it since the sequel crashed and burned, which is sad because no game has really given me the same atmospheric vibes. It was (is?) really special

Nox

Timesplitters

Def Jam 1/2

Amplitude

Ogre Battle on the SNES is the original auto-battler. I would really recommend Ogre Battle 64 though, not only is it one of the very few RPGs on the system but it's got really unique gameplay. It's got its flaws but I'm such a sucker for the character designs and job/class system that it's still my favorite game to this day.

I recently got a ps2 and all of the SOCOM games. I’m still working through the first game, but I think 2 was my favorite back in the day. It’s the only game I was aware of at the time that enabled voice commands to the AI, and the first one came out in 2002 I think. i wish they would reboot the series.

I'd heartily recommend Fallout 1, with a less enthusiastic recommendation for Fallout 2

I played the first splinter cell a few months ago. It was honestly really really fun and rewarding, but there were aspects that showed its age. Some of it was trying a bit too hard to be immersive and even on lower difficulties the enemies were brutally aware of their surroundings. There are also like two checkpoints a level and each level can take upwards of an hour depending on how slow you go. Otherwise I thought it was a really fun game and the sound design was out of this world for its time

Heroes of Might and Magic 3 is one that instantly comes to mind. It surprisingly still has a very active competitive playerbase, mostly comprised of slavs that have been playing it since they could read words on a computer screen. Another one that I've personally can't stop playing, is the first Warhammer 40K:Dawn of War game with it's expansions and mods. It's just so good, and I wish a modern version with a modern engine could be made. I don't trust Relic to do that tho.

Other than that, there's a myriad of old console and arcade games that are still excellent. Super Metroid, SEGA Rally, shmups like Dodonpachi and Mushihimesama, Street Fighter 3: 3rd Strike... there are really way too many to count.

The original Leisure Suit Larry series, Monkey Island, Day of the Tentacle, Myst, Half-life, Doom, Quake, Lemmings, ... For more fire up your retropie or recalbox on a raspberry pi.

Vanquish, best "cover" shooter that I've ever played, really wish it'd get a Switch port and that Platinum would revisit it.

Sliding around on jets, going into slo mo to hit weak points, vaulting cover and initiating slomo, it's all so fucking fun and visceral.

Skies of Arcadia. Two words: sky pirates. Coupled together with a beautiful overworld filled with hidden discoveries, charming characters, fun ship combat, and excellent music. You can’t go wrong with either the original Dreamcast version (higher quality music, VMU minigames) or the Legends remastering on the Gamecube (an additional story quest, less frequent random encounters - the original is somewhat relentless with these).

Gothic 1 and 2. Weird control scheme you have to get used to, but very good games world building snd character wise. Can be quite challenging with the combat, but quest allow tons of ways to solve problems.

Alpha Centauri. Just reading through all the wonder quotes and worldbuilding is amazing.