Short but interesting games:

• Antenna
• Sisyphus Reborn
• A Raven Monologue

https://store.steampowered.com/app/449140 - Istrolid
https://store.steampowered.com/app/314010 - Boid
https://store.steampowered.com/app/489560 - Astroflux
https://store.steampowered.com/app/708420 - Broken Grounds
https://store.steampowered.com/app/204300 - Awesomenauts
https://store.steampowered.com/app/578310 - Brain/Out
https://store.steampowered.com/app/649770 - Coregrounds
https://store.steampowered.com/app/560260 - Super Blue Boy Planet

https://store.steampowered.com/app/223710/Cry_of_Fear/

Awesome campaign.

The Monster INside
Disturbed
Port of Call
Also, there are surprising amounts of great free to play horror games, if you're for the narrative - point and clicks, RPGmaker games, visual novels - they need to do the writing well to get good scores as a free to play game. It's really worth diving into that part of the store! :)

Thanks for the list, was coming to add Coloring Pixels, but already up there :P

Emily is Away :)

Quake Champions F2P
https://store.steampowered.com/app/611500/

Thanks.

Meteor 60 Seconds!

A fun and ridiculous game.

Perceptions of the Dead
Little suspense/horror VN stories - 3, each about 10ish minutes long. Pretty good art and voiceacting - the dev has a 2nd episode that looks fun (Though not free to play)

The Expendabros

8-bit Bayonetta had it's store page removed but you can still download with this link: steam://install/567090/

SNOW was a really fun f2p game but they locked the main mountain (Sialia) behind a pay wall and MP servers were stuck in slow motion the past few times I tried to play. There is still a lot of fun to be had and there is always a chance this week's mountain will be good (maybe even Sialia if you are lucky!)

relic hunters zero is also great

Path of Exile

Mini Battlegrounds

How about Deceit - https://store.steampowered.com/app/466240/Deceit ?
And Atlas Reactor - https://store.steampowered.com/app/402570/Atlas_Reactor ?
Short one - The Old Tree - https://store.steampowered.com/app/346250/The_Old_Tree/
Cool one - The Expendabros - https://store.steampowered.com/app/312990/The_Expendabros/

Electric Highway, its short but have a nice soundtrack in my opinion and I enjoyed it while it lasted, highly recommend it.:)
https://store.steampowered.com/app/412140/Electric_Highways/

(allright its more like an experiment game than a full fledged one, but still its cool)

https://store.steampowered.com/app/744900
Dead Frontier 2

I feel that Doki Doki Literature Club! is being ignored here and it's actually a very interesting game.

https://store.steampowered.com/app/698780/Doki_Doki_Literature_Club/

Shrouded in Sanity

The free version without steam features...:
https://store.steampowered.com/app/820400/Shrouded_in_Sanity_Freebirth/

Oh, mini Battlegrounds wasn't free before! Im in! :)

Lake of Voices
A horror/thriller visual novel about a group of travelers crossing a very unsettling lake. Been playing it these past days and I got nothing but praise for it, good story, good voice acting, very worth checking out 👍

And Path of Exile deserves to be added to that "not hidden F2P games" list, by the way :)

https://store.steampowered.com/app/910460
Rocket of Whispers: Prologue

i will organize the list soon, sorry for not updating it yet but I have been busy lately.