The acting is good, but the story just veers all over the place.
So, spoilers ahead, obviously:
First it kind of meanders along with nothing happening, then it goes through the usual horror movie tradition of everyone doing the dumbest possible thing they could do so that they can get killed off. They bring a bunch of "experts" for this expedition but then everyone just wanders around in the woods. Why did they need a primate specialist for this?
Then for the last 15 or so minutes it super abruptly and randomly turns into this gross, disturbing mess of gore, complete with some backwoods hermits eating people, dancing with corpses, and alluding to keeping the surviving woman alive to rape. It feels like this drags on forever and it's such a weird, sharp change of tone.