For something that clearly seems to be one's first attempt at designing an fps with multiple levels (gotta give credit there), I thought this was okay.

My advice if you want to try another fps, more walls and cover would be nice as well as some guardrails to shield from the precarious bottomless pits so the player has the option to retreat somewhere they won't be shot at from all directions (the fifth and sixth levels are the biggest offenders imo). Also, if you want the guns to have infinite ammo, make them behave like power-up pick-ups instead of letting them all be used at any time against any enemy because there's no incentive to use anything other than the machine gun aside from the long weapon reload times. 

I do also think it's weirdly redundant how unlocking cages requires keys but the player is given all the keys they need right at the start and never needs to collect any in all of the levels. If expanded, this could become a fun little Metal Slug riff (with ghosts).

Nice! Lot of content in a small time frame :o

I'd say the first feedback that came to my mind is that the mouse sensitivity was prety low. For me, what made the game really hard was that I had to move my mouse a ton to turn the player, maybe you could add a mouse sensitivity option ? 

I appreciate both the number of levels and the variety of ideas explored within them! A lot of mechanics were implemented in the time available and it gave you the space to experiment which is admirable!

I was not a fan of the tutorial level although I do appreciate that you have one. Having worldspace text is great but try not to allow the text to overlap on the screen. You could have blocked the player's eyeline using the maze walls from later levels and more progressively exposed the player to concepts rather than dropping the player onto a plane with all the game rules.

Personally, I would have picked a different level order. Being dropped onto a plane with several ghosts as the first actual level resulted in my repeated death as I figured out how combat worked. Pretty high stress environment with nothing to hide behind! Perhaps the first maze level could serve as a neat introduction to combat with ghosts.

I'd introduce the ghosts one at a time too; make a bigger thing about what makes each of them different. They clearly are different; don't be afraid to take a level to just show off what you've done to make them interesting.

I noticed that the ghosts fired physics objects while the player fires raycasts. This lets me cheese them by standing just next to a corner that they can't fully shoot around and shoot the edge of their hitbox. Perhaps not the intended gameplay. I'd be tempted to remove the collision with the ghost projectiles and the environment and just say "Well they're ghosts. They're well known for going through walls!" Just be sure to introduce that idea before making it a question of life or death.

I liked that some of the levels felt like a puzzle while others felt like a more traditional shooter experience. I did get lost a few times in the bigger, emptier maze but it was super cool to see multiple styles of gameplay going on!