Finding gems in the world of FOSS can be a difficult task if you don't know what you're looking for. However, I can easily say that my top three are Antimine, Shattered Pixel Dungeon, and Minetest.
Antimine is your typical minesweeper game but it's really well-produced and customizable. I hadn't really played minesweeper much before Antimine, but I find myself picking up Antimine pretty often.
Shattered Pixel Dungeon is an awesome roguelike that proves rather challenging. The more you play it the better you become, and sometimes you'll get some really great RNG and it just feels awesome.
Minetest on it's own isn't much of a game as much as it is a 3D block-game creation engine. It's more or less the bones that make up a FOSS Minecraft, and with projects such as Voxelibre, it is a really fantastic Minecraft alternative!
What games do y'all play from F-Droid? Feel free to mention things that come from other repos than the ones that come with F-Droid out of the box!
I think FOSS is uniquely awful for game development. I applaud anyone willing to donate their time but when it comes to games I much prefer pay-once as an attribute to focus on.
Game devs need to eat and donations are unreliable (I used to help run a community funded MUD - we admins often ended up paying server costs out of pocket) so I focus more on finding good games that avoid ad or microtransaction based revenue models so the most reliably good games I find are either shareware/demo before you buy or just a straight up cost.
I definitely appreciate OSS games though and there are good non-free OSS games out there, most people aren't dicks that reshare the source after purchase.
I like the approach of old id games. Sell the game and after a few years open source the engine. That way the developers keep getting paid for assets and the community can keep the game alive on every platform imaginable.
Maybe, but what I miss from shareware is that I would get a game (e.g. Quake, Duke Nukem) from someone and be able to play without restrictions the first chapter.
In fact, most shareware games had also multiplayer available so those were very common in school's computer "labs".
Freemium apps, in my experience, have too many ads and fiendish tactics to my taste (Though I know it's not all of them).
I usually like puzzle style games so it may not be to your taste. But, I'd highly recommend all of these - the first one in particular is quite a hidden gem.