Very clear marathon influence, the texture work is fantastic but the weapons are a little too low-res by comparison. I think some black or gray distance fog would also help build some more atmosphere.
You’ve got a door on the second level that doesn’t look like an interactable type, yet it is.
Then on the fourth(? I lost count) level there’s this door leading to a black wall.
I ended up just stopping at some point. The game is a solid foundation but the slow pace, limited roster of very easy enemies, and repetitive environments make it feel like a chore.
Surprised you managed to squeeze such a small game package out of Unreal, and the Linux version even works properly, kudos!