The game is really difficult in my opinion, but it's the kind of difficulty that does not rise from concious game/level desing itself; it's the one that comes from unbalance. I always have trouble balancing my games too, since I can never find someone to playtest them decently, so I know very well that it's a difficult thing to achieve.
There are way too many enemies and the weapons are not effective enough to stop them. They also feel really repetitive, given the lack of shooting feedback and the fact that they just shoot perfectly straight, without random imprecisions. Making a first person shooter the "right" way is quite a difficult task for such a short amount of time, so it's totally comprehensible that there are things that are not polished enough.
I didn't really enjoy the very long and extremely in-depth tutorial either. Explaining the setting and the controls would have been enough (the part in which you explain that you have to parkour your way around the fences was also quite needed).
I'm sure you'll manage to build upon this and improve it with time, good job!