I made the cut-off 95 percent positive since that's what Steam calls Overwhelmingly Positive (but you have to have a certain number of reviews to qualify). A couple of these are not complete games but are first chapters or a free version of a full game (generally means there are a few unnecessary things left out). I did not include prologue games, as they are often uneven in how much of a game you actually get.
store.steampowered.com
95 percent: Free-to-Play: Looks like multiplayer Dig Dug to me.
store.steampowered.com
98 percent: Free (it's the first chapter only): RPG/Psychological horror. I LOVE the graphics.
store.steampowered.com
95 percent: Free-to-Play. Looks like a mobile game, but people seem to like it.
store.steampowered.com
95 percent: Free: Adventuring and tavern running.
store.steampowered.com
98 percent: Free: Arcade-like physics (and other things) simulator
store.steampowered.com
97 percent: Free: Gothic racing. @Frindis another one you might be able to make a tournament out of
store.steampowered.com
96 percent: Free: Horror

Arcanists on Steam
Players take turns in a race against the clock, utilising an array of spells to defeat their opponents in battle! Victory is accomplished by becoming the 'last man standing' (or last team) after all other players have been reduced to zero hitpoints.

Illusion Carnival on Steam
A lost soul wanders through a whimsical, eerie pop-up book like amusement park. Dive into fun-filled stages, encounter unique characters, fend off spirit erosion, and uncover the park's hidden secrets. The enchanting yet dark Illusion Carnival begins now.

Save 10% on Horticular on Steam
You have been magically summoned by mysterious gnomes to restore a long-lost garden. Attract adorable animals, build a lush environment, and immerse yourself in this relaxing garden-builder. Will you manage to reclaim the wasteland or succumb to a looming corruption?

Ale & Tale Tavern: First Pints on Steam
This is the free version of the game "Ale & Tale Tavern". Get ready for a thrilling mix of genres: a cooperative, first-person, open-world fantasy tavern simulator, action, fishing, hunting, exploration, and completing fun and diverse quests. And, of course, COOKING!

The Powder Toy on Steam
The Powder Toy is a classic physics sandbox game, which simulates air pressure and velocity, heat, gravity and a countless number of interactions between different substances

Nightmare Kart on Steam
Zoom through gothic streets in this horror themed vehicular combat racing game!

[Nightmare Files] Clap Clap on Steam
Clap Clap is a short indie horror game that puts you in the shoes of a house sitter, experiencing strange occurrences in a seemingly ordinary home.