The Isle
My friends and I have been playing a lot of The Isle over the years, a dinosaur survival game, and recently we've been checking out the new updates. Gameplay is simple, run around, eat (veggies if you're a herbivore, other dinos if you're a carnivore) and try not to get eaten. There are also breeding/nesting mechanics.
The game has strong horror elements. Nights are extremely dark, other dinos can jump out of dense vegetation without warning, while drinking at a river a gigantic Deinosuchus might suddenly breach the water and drag you under, etc.
The focus is mostly on realism, there are few fancy arcade mechanics/skills/etc., just you surviving and growing (which provides benefits to attack strength, but often makes it harder to hide and your food requirements increase with growth). It's great fun with friends, but I also had a great time roaming around alone or forming groups with strangers (there is an ingame chat but it's even more fun to only use the various calls, grunts and screams to communicate)
If you were to download the game make sure to use the EVRIMA beta branch. The stable/default branch (i.e. what will be downloaded if you don't change anything) is basically the "old" game, that sees no more development (AFAIK). EVRIMA is a much improved version, even though it doesn't have all the dinosaurs of the old version (but some new ones). The screenshots/videos on the Steam page are the old game, which doesn't really represent the current status. For a taste of what it actually looks like these days I'll include a video from one of the recent updates below.
They're also working on including humans and human settlements into the game, and I think there already is a testing branch available for that (which I haven't tried yet). I also have to mention that the latest update, which ported the game to the new Unreal Engine version, seems to have introduced some graphical issues (especially when it comes to water, which looks much worse now) and the networking code seems laggier than before. Hopefully that will be fixed soon.
edit: forgot to mention that I play it on Windows currently (because I first installed it there and disk space constraints keep me from moving games to my Linux partition atm), and protonDB only gives it a Silver rating