Wasteland 3. A tactical CRPG with pretty decent combat mechanics, amazing presentation, and an interesting setting full of numerous choices. Some choices are clear moral dichotomies, but many of them are presented much more ambiguously. A really excellent game for people wanting the feel of a CRPG. I like it better than Wasteland 2 (although that game is also good), because WL2 while good throughout tends to overstay it’s welcome, presentation is somewhat dry, combat is not as interesting, and the stat system is slightly more bloated than is comfortable.

The Outer Worlds. Much more well known in the mainstream, although I think unfairly maligned. There was a lot of initial hype leading up to release, as people compared it to Fallout New Vegas. The game itself has a Gilded Age aesthetic which does make the comparisons very surface level similar. The game as presented though is structured less like a Todd Fallout and more like a classic BioWare RPG. Rather than a full open world(s) game, your ship transports you from location to location, and each destination is a smallish curated area densely full of quest activities. Combat is something in between FNV and Fallout 4, with numerous quirks of its own. The companions and setting are the stars of the show, so if you want a whole game of that aesthetic you’ll greatly enjoy it.

Tunic absolutely blew my mind. If you get the chance and love old school top down action with a twist (this game forces you to think) you might enjoy it.

Vault of the Void: A Slay the Spire-like roguelike deckbuilders, but with enough of its own ideas. For example the decksize is fixed at 20 and you gain a booster containing 5 random cards in the beginning. You also can see the encounters and the card rewards before the battle, so you can adjust your deck to each fight if you want.
Gordian Quest: A mix of deckbuilder and rpg where you play a party of up to 3 characters each with their own deck and battle either through the campaign-mode or a Slay the Spire-like roguelike mode. The cards are influenced by attributes and traits that you gain from leveling up and gear.
Dream Engines: Nomad Cities: A survival city-builder where you extract ressources from maps and defend your city against attacks. What differentiates this from other survival city-builders is that your city can fly, and so you can/have to leave once the monster waves get to strong.
Astronarch: A roguelike autobattler where you build a party and autobattle your way through a Slay the Spire-like map to defeat the final boss. Artstyle looks like it was created with the help of ms paint but the gameplay of creating combos between your heroes and items is really fun.
Marvel’s Midnight Suns: Not exactly an unkown game, but I think a lot of people skipped over it because of the Marvel branding. The mix of card-based and tactics combat is the absolute star of the game. And regarding the marvel stuff: Some characters grow on you, especially if you can laugh at how over the top some of the superhero stuff is, and for the rest there is a skip button. Also works well on the steam deck which made it one of my favourite games for when I am travelling.

https://store.steampowered.com/app/1318690/shapez/

Shapez hopefully counts as “not popular”. It’s a completely chill factory builder (think Factorio with less complexity and zero pressure/resource constraints) whose difficulty continues to increase. Pretty fun.

https://store.steampowered.com/app/960690/One_Step_From_Eden/

One Step From Eden is a MegaMan Battle Network style rougelike. Fun to make builds, but then you get to start again shortly after(cuz it’s hard)

https://store.steampowered.com/app/1062090/Timberborn/

Timerborn is in Beta and is constantly getting more content and QOL updates. It’s a beaver themed city builder to survive droughts.

Seconding ASCII Sector as well. Basically Privateer’s Gemini Sector world with the gameplay expanded and of course ascii based and more rogue like. Tons of fun.