here is my demo (first run)
 https://drive.google.com/file/d/1B2N0Pt23sVMYrvW00Y3HFCk6EqmQ0T33/view?usp=sharing
 
 For a first map the brushwork and lighting is really nice.
 The path of the player is sometimes confuse but it's ok you know where you need to go.
 
 Adding a void, space or cloud skybox could be cool on this map.
 
 I'm not a good player so I play in skill 1
 I couldn't finish the map the end is too hard : 
 You put a shambler and a huge green shambler in a room where you can't hide with other enemies around, It was impossible to survive the end for me. (I'm waiting for others demo to compare :D)
 
 I didn't understand how to get the yellow key. 
 I did a rocket jump to take it but I'm pretty sure that's not the good way.
 
 Anyway the rest of the gameplay is good, even if I hate platforms. (it's stressing me so much when i'm recording a first playing demo).
 
 Great job for the rest. I'll watch for your next stuff !