It's a dinosaur hunting game. You get a rifle, you're plopped on an island, and you have to kill dinosaurs. Once you run out of bullets the hunt is over.
It's meant to be a somewhat realistic hunting simulator, with the dinosaurs having somewhat realistic behaviour. But all that really boils down to is that they have a drink sometimes. They can smell you if the wind blows your scent their way, and each dinosaur has different sight/hearing stats, so some can see you far off etc. You start off just hunting Stegasaurus, but there's 9 types if dinosaur you can eventually hunt I think, as well as a couple smaller dinosaurs just running around.
You get gems and points for kills. The better the kill, the more points. Points continue to add up and unlock more levels. The gems are used to buy all your upgrades and hunting licenses. If you shoot a dinosaur you're not licensed to hunt you don't get anything for it. The way the gems/upgrades work is pretty cool, in that they're all temporarily equipped. If an upgrade costs 20 gems, you lose 20 gems while it's equipped. But when you unequip it, you get those 20 gems back. This means you can try out most stuff quite early on, although licenses cost gems, so you always need some invested in that.
There's upgrades to highlight dinosaur tracks, make you harder to see, remove your smell, give you more ammo, etc. Most of these reduce your score by 5-10%, so there's some incentive not to use them. The one that shows nearby dinoaurs on your GPS reduces your score by 35%. You can also use sleeping darts if you want, and there's a crossbow and a sniper rifle.
Without the most helpful upgrades it can be a slow and frustrating game, as some dinosaurs will see and you run off before you see them, and you end up just walking around doing nothing a lot. But then if you want to play it like a serious hunting simulator I guess that's part of it. And if you want to use a few of the good upgrades at once you need to put the work in hunting normally to get enough gems, or sacrifice a few of your licenses. Overall it's pretty well balanced.
And you get to kill dinosaurs.