Looking for lesser known action-adventure games

I can't help with a recommendation, but you could always search the Steam store for story rich, action, adventure, select "games", and sort by rating. Then you can scroll down the list skipping the ones you recognize and check out the highly rated ones that are new to you.

I think this link should do that:
https://store.steampowered.com/search/?sort_by=Reviews_DESC&tags=1742%2C21%2C19&category1=998

Middle-Earth Shadow series? Despite not being exactly what you asked, OneShot has a similar premise and is great!

If you aren't bothered by older games I can recommend you:

Jade Empire, The Saboteur, Psi-Ops: The Mindgate Conspiracy, Infernal, Second Sight, Total Overdose, Shadwen.

I checked your library and you have a lot of cool games that you haven't played. I enjoyed playing these games: Resident evil 4, Bioshock, Mad Max, Spec Ops: The Line,Fahrenheit: Indigo Prophecy Remastered, Castlevania: Lords of Shadow.

Two Worlds / Two Worlds II might fit what you're looking for.

Binary Domain
Enslaved
Killer is Dead
Ruiner
Remember Me

Risen
Arx Fatalis
Blades of Time

Deadfall Adventures

This one was probably on IGN, but PROTOTYPE is extremely good.

Right off the bat:
Bound By Flame
Hunted: The Demon’s Forge
Darksiders 1-2
Dragon's Dogma: Dark Arisen
Tales of Zestiria / Berseria

Some early Spiders's games might be a good fit:
Mars: War Logs
The Technomancer

While not the direct sequel/prequel, but both should be placed within the same universe.

You may enjoy Bound by flame or Greedfall (not really unknown) if you liked Dragon Age. Also can recommend Elex.
Also someone recommended Risen, can be good choice, also if you never played Gothic, it is good time to start, cause THQ wants to do remake of game.

it's a world war 2 setting, and not text based but more Tomb Raider style, but The Saboteur on gog might fit.

CrossCode perhaps? I mean, I wouldn't call it casual and it does have some very elaborate combat and puzzles (it does have the options of lowering the difficulty significantly). But it also has a really good story, rich setting and likeable characters.
I dunno- check out the Demo if you want. (It's pretty outdated and only covers some of the tutorial but it should give an idea of the game's setting.)

Alpha Protocol is awesome according to some, and horrible by others, for me it was super enjoyable. Give it a try if you want some secret agent action. ( Just mind that accuracy is heavily affected by your skill with the respective weapon, you can keep your crosshair on someone's head and still constantly miss if you re untrained with the weapon)

For me, Enclave is one of those gems that are hidden in plain sight :D
So many people own it because it was bundled and given away for free multiple times, but only a few actually gave it a try I think :)
I played it a few years ago and I still have fond memories of it :3

It is not really a lesser known game, but maybe Deus Ex: Mankind Divided.

Killer7 comes to mind. It's arguably not much of an RPG, but it is a story heavy action/adventure game.

I suggest looking through a database of PS1 and PS2 games. You can find a lot of old forgotten stuff there, Much of it isn't for sale but you can emulate most of it if you have a decent computer.

Vagrant Story is a good one too.

Skyrim Special Edition
Fallout New Vegas
Fallout 4
Witcher 3 Wild Hunt has a good story as well

Beyond: Two Souls, although I wouldn't call it lesser known.

Disco Elysium?
3030 Deathwar Redux - A Space Odyssey

Here's few ideas...

Apsulov: End of Gods
Beautiful Desolation
Bound by Flame
Demonicon
Divinity 2: Ego Draconis
Drakensang & Drakensang: The River of Time
Gujian 3
Kenshi
Mars: War Logs
Outward
Pathfinder: Kingmaker
Risen 2 & Risen 3
Seven: The Days Long Gone
Shadowrun: Returns
Spellforce 3
Tainted Grail
The Technomancer
The Waylanders
Tokyo Dark
Tower of Time
Zoria: Age of Shattering (Upcoming)
Solasta: Crown of Magister (Upcoming)