I did a whole playthrough, I think it was pretty good. From the get go I see you planned to have a certain flow of combat maried with exploration. Small pickups by the broken boat, enemies hiding in the bushes, ambush by the gate, jumping down to be ambushed by headliess dogs. I liked the level design for the chieftan, the idea of desolated and flooded construction site was pretty neat, going up and then moving between buildings,either you have a natural talent for levels or it took a lot of planning to make it good. The chieftan was a motherfuck, does too much damage and is a damage sponge himself, pls nerf. Too much grenades thrown at his second phase, his ground pound shouldn't be that powerful I think. Grenade launcher has a very low splash damage and I'd expect it to be end-it-all when it hits enemies point blank, but normal shielded enemies were almost immune to the explosions. I had two health mutagens that could heal me very fast, very powerful, so I liked it a lot, but I expect you to nerf it or have this mutagen more costly or maybe even tiers, so 1 mutagen to heal 2 damage, another mutagen to heal 4 etc. Your basic spear-chugging enemies are way too accurate and spears should lose their height faster.
Graphics and animation are serviceable, but I'm afraid it's not enough. The most jarring are spikes, just rows of neatly ordered triangles. I didn't like the animations for human enemies too, they're very basic. Pickups are very bright which on one hand makes them easier to find, but they also stand out from the surroundings a lot.
Regarding lore, if mutations make people devolve then why are we injecting ourselves with them in the first place? When going out for hunt aren't we just risking being turned into mindless beasts ourselves? And since people devolved why they managed to form tribes and even cooperate with other animals? There are some general questions I had when playing the game. Not everyone is cooperating of course, red-handstanding guys and the mutated elephant killed the default badguys, sure, but other than that I don't know why they'd form an alliance. Maybe I'm reading too deep into it.
I was thinking that maybe with smaller levels and some randomness in them you could have a very enjoyable roguelite - levels with different amount of enemies, supplies, random order and events spicing up the gameplay, with bigger levels, like those in this demo, as milestones. Add mutation research, find new "blueprints" for new mutations and ingredients on levels to give additional incentive for exploration. As a linear game it might not be as fun and replayable.