Nice to see a FPS entry!
The controls are very nice and responsive, didn't have any issue with movement or platforming. You might want to add at least a blob shadow underneath the player, as a kind of visual feedback on where they would land.
Other than the double jump, the sound were all very nice and fitting, both ambiance and SFX.
The graphics were nice, and I'm quite pleasantly surprised how well the lighting and fog made the limited amount of textures work this well.
The biggest issue I had with the game, we're the enemies. Most of the plants ambush you, and the... quill armadillos? have such fast moving projectiles, that it's impossible to outmaneuver or hide from them. One advice given for ranged combat focused FPS games, is to make the enemy fire projectiles, instead of using hitscan, so that the player has the ability to avoid taking damage.
The path blocking rocks, could also blend a bit less into the environment, especially if they hide the critical path.
I don't know if there is a reason for the doors (background loading, instanciating, etc) beyond separating rooms. but if they're only there to divide space, they should open way more quickly.
That all said, would play more, with less cheesy enemies and more combat.