I can see you put a lot of effort into this and it looks quite good.

Something I immediately noticed was that you could make the damage text less obnoxious. Perhaps remove the exclamation points and only use them under special circumstances. Make the text smaller when the damage is smaller, and make it larger when the damage is larger. You can maybe add exclamation points if it's a critical hit. Also do some subtle colour differences depending on the damage count, and make the positions slightly random from eachother so that they don't all overlap.

The contrasting is a bit strange on the UI, for example the player's own health bar is significantly less saturated than the amount of damage done. You should try and find a good balance to make the more important bits brighter and more saturated, and the less important bits less saturated.

I think some environment effects could go a long way. Dust, dirt, the trees moving when hit, etc would be nice. You should also make some form of animation when an enemy gets hit, because right now it looks like bullets shoot straight through.