Nicely detailed first map with competent use of different monsters to create different gameplay setups.
The first secret locked me out because I wasn't standing in the right place when I opened it. Later I found it crushed me because of the tight scale (scale is something that most people struggle with at first). I also found there was unnecessary use of clip: generally it's best used to prevent the player getting stuck and not to block off areas. I liked the way you had partially broken architecture, that's something which we don't see enough and somewhat helps to break up the symmetry. In terms of visuals, it could be a bit darker. Another thing to watch out for is your use of button textures, as generally the red ones are only for shootable buttons, but you've used them for both kinds of button in this.
I'm looking forward to your future maps, and hope you stick around!
