If you are talking about multiplayer :

• The Finals
• Insurgency Sandstorm
• Hunt: Showdown 1896
• Hell Let Loose
• CS 2
• No More Room in Hell 1&2

Many options !

I can recommend Selaco. It's built on GZDoom and one of the best shooters I've played in the last years.

store.steampowered.com/app/159…

Selaco on Steam

Selaco is a brand new original shooter inspired by classics, featuring thrilling action set pieces, destructibility, smart enemies and a fleshed out story taking place within an immersive game world.

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Anger Foot natively supports Linux, and I'd consider the gameplay loop to be pretty casual.

To sum it up, you kick down doors and shoot your way through rooms while having hardcore EDM blasted at you. It has a Hotline Miami vibe to it, but is FPS.

Trailer with gameplay footage

Anger Foot Launch Trailer | Out Now on PC

In this brutal, breakneck first-person booter, the Anger Foot introduces the ruthless gangs of dystopian cesspit Shit City to a fury of feet and firepower.Th...

^YouTube

Ravenfield for cartoony/low poly acradey fun

Operation Harsh Doorstop for something more like Project Reality

Would run and gun games count? If so, I strongly recommend the Neo Geo Metal Slug games. They're all sold emulated on PC (GOG for the no launcher requirement).

And on a more usual sense of "shooter games", Saints Row The Third (GOG and Humble Bundle) and UNLOVED (original version is a mod of Doom II afaik). And just a note, Saints Rows The Third, from some tests I did a while back, seems to have a memory leak issue in character customization screens when running under default Wine.

I have tried all these on Linux through proton.

Dusk - the OG boomer shooter revival game, should be the first game to try to see if you like these kinds of fps.

Amid evil - beautiful looking FPS instead of firing guns you fire unique magical weapons.

Ultrakill - extremely difficult movement shooter with a very interesting setting and lore. Its still not fully complete theres like a final layer thats still cooking but what's there is worth experiencing.

Selaco - FEAR inspired FPS built in GZDoom somehow. Tight movement, great gunplay, interesting enemy difficulty progression, superior AI that will flank your ass and hammer you with what feels like tactical actions, great interactive environments.

Turbo ultrakill- one of the most fun and bombastic FPS ive ever played. Play as a merc who gets turned into a living chainsaw as you ruin the plans of wannabe trancendent techno gods and run away super AI one bullet at a time

Cultic - plays heavy into blood and residents evil 4 inspirations to deliver a very mood atmospheric FPS with the best goddamn dynamite throwing mechanics since OG Blood itself. The single dev is really passionate and is constantly sharing updates to episode 2.

Ion Fury + ion fury aftershock
A love letter to the best parts of build engine games of the 90s. Its incredibly well made build engine game with huge sprawling enviroments and too many secrets. The pistol with auto-lockon is hands down the best pistol Ive every used in any game. Aftershock DLC is even better than the base game.

Zortch - another passion project made by one person with an in-house engine coded just for the game. The enemy AI moves around a lot and the cartoony graphics and plot make it more of a light hearted title to have fun with like a game you would find on the N64. Its only 5$ and easily worth it.