Steam

Deadlight, from Tequila Works. I bought it for less than $3 on a whim (might have even been $1) during a Steam Sale on the last day, because "Why not" I thought. Then I actually gave it a shot, and it turned out to be really good. Especially surprising since I don't normally like side scroller puzzles with action elements. The difficulty was just right, and the forgiving checkpoints did away with the usual frustrations I have with games like this.

SNKRX for me. Minute to minute gameplay is very simple -- all you do is steer your train of dots left and right around a small arena, but the depth of strategy and the skill cap is surprising. I got many hours out of it. Also there is a mobile version!

icey. i literally only bought it for the £5 steam link, but it's actually a really good hack&slash platformer with a stanley parable-esque story. i'd recommend anyone who has it languishing in their library to give it a go

Lots of Valve stuff - Portal 1 / 2, the Half Life games, and Left 4 Dead 2 all go on sale for like a dollar very often. Team Fortress 2 is flat out free to play, if you're willing to either pay like $2.50 for an item to unlock your account or put up with a bit of f2p bullshittery. Put almost 4000 hours into TF2, it's my all time favorite game.

Ring Runner.

The game is mind blowingly well made. Incredible tutorial, fun story, co-op, multiplayer with self hosted servers, customize 14 different integral parts of your ship with 20 meaningful customizations each.

I bought like 20 copies and hand them out to anyone whenever. I got the book for it, which sadly isn't really well written... And kickstarted their next game Pop-up dungeon.

Legitimately best $1 I ever spent on a game and that includes to the moon.

Ultima IV: free on GOG, one of the greatest games ever made that still holds up today (though irritating in certain ways, the core game is pure gold).

How about $0 for CS:GO?

I have not spent one red cent on that game and I have 1600 hours on it.

Supraland, I 100%ed that and the dlc, I hadn't done that since Spyro 2 on the PlayStation.

The Vanishing of Ethan Carter also left a big impression on me. The ending keeps lingering in your mind. I think a lot people reach the end of the game without doing the side quests, when it turns out the side quests are what trigger the ending and the credits to roll. Just sit there in silence after the credits are done running kinda game.

Prodeus just kept on giving, also recommend. Doom on steroids.

Reflex Arena, which is the best arena shooter with classic feel. It also has that classic amount of players, which is none, which is a problem for a multiplayer game. Only recommend if you are a hardcore Quake fan and have friends, a rare combination.

Auralux is a very relaxing "RTS" reduced to the bare minimum. It's a great game. Many states of varying difficulty.

Most people would probably enjoy auralux and supraland the most. Especially auralux can be very soothing.

KOTOR. Bought it in 2012 for 2.24€ during a steam sale, not only I'm still playing it to this day, but its plethora of technical issues pushed me to learn new things about how linux works internally.

I got Rocket League for like 5 bucks. Didn't touch it for a long time. Starting playing during the early COVID lockdowns. I got HOOKED now have nearly 1200 hours in it .

I may have paid more and it is not necessarily my favorite game but I was pleasantly surprised with I Am Alive.

ZZT on shareware
https://www.dosgamesarchive.com/download/zzt

Why would that make you angry?

Gary's Mod!

Insurgency. Insurgency:Sandstorm. And now…Battlebit