The overall experience looks amazing. Shaders are great, post-processing effects are great, the simplicity and color spread is great.
I am not sure it is necessary to have the player hold the mouse button to aim though, the scoring system could use a bit more of an incentive (Though having an online scoreboard at the end is GREAT), and I really wish the bullets had a bit more of an "oomph" to them.
That was fun and enjoyable, I loved it, great work!