Good job! I enjoyed the experience overall :)
Things I liked:
The intro was my favourite part to be honest, was a really nice introduction.
Also the boss's appearance was great. I enjoyed the way you get life and concept of weapon changes.
The sequence of traversing a building had good flow (although at first I was confused by being on floor -3)
The main menu had a nice style too.
Things I didn't like:
The audio was a bit too much for me, especially with the one gun that spams bullets it's just really loud constant firing.
The boss fight was too easy with all the life pickups and cover.
Bugs:
1.I had a bug where I was shooting when I died, and it didnt stop the shooting sound.
2.It also didnt seem to take me back out or do anything when I died.
3.Pressing esc and starting again respawns you onto the same level you were on last. So when I died, I spawned back where I died. I say it's a bug because I was expecting start to restart from the bottom (not sure which behaviour is intentional).