Liked the idea, like the art and Especially loved the story. I'm a big fan of space.
But I'm sorry to say, I didn't enjoy the game. I turned it off before the end because I was doing the first 3 levels over and over again. I accidently pushed a bolder in The Mantle Level down the corridor of another bolder. Which got me stuck and had to restart. And at the end, had no clue what I was doing (Which is the point because of the mission). But means that there is a high chance of dying which means I had to replay previous 4 stages twice. Because I needed to kill off one of the dudes to pass a level and that only lasted for one guy. Plus it got tight when it came to oxygen. Did see that there is a plant that gave oxygen, but I was hesitant since every other plant was killing me.
I think it can be greatly improved if the plants that ate the player, so the next player can walk on top of them. Stayed in that state for the entire game. Which means if players died at the end, they can just go back to the end level without worrying about anything else. And if they happen to die, that's on them. Also bread crumbs would be nice. But that could either be by choice or time constraints.
Enough of the Problems and lets get to the good bits.
Level design is smart, like how later levels got more paths and confusing. Giving the feeling of pressure when you get lost and start to run out of oxygen. There are lots of mechanics that were implemented for a short amount of time. Plants that explode, plants that eat the player, plants that give oxygen back, moving boulders, climbing walls and of course the dying and coming back to life (Technically). Sound design sounded great, felt immersed in the environment but also had that 8 bit feel.
I'm sorry that I wasn't to play at the end, especially the amount of work that you put into the game. But I hope this review helps. I don't want to leave a bad comment and make you feel bad, but also want to be honest. Hope this helps.