Overall I think you did well bringing together these premade assets to make something that looks visually consistent! I think that if you were to just tone down the bloom and chromatic aberration a smidge, as well as reduce the FOV to say ~80 degrees, then the game's style would be able to shine more and be less overwhelmed. I like the choice to place the UI in the 3D space, but typically in other games to maintain readability it's scaled to always take up the same space onscreen. I quite like the visual FX of the shots and their impact, think it's just missing some damage flash on the enemies and maybe a death sound effect. The sound of the shots has good impact, just needs a little variation in volume/pitch to make it sound right in action. I wonder if maybe a better way to present the gameplay, given the 3D cursor and turret defence, would be to use an overhead view that didn't turn with the player character? I do like how the player character feels like a hefty hunk of metal!
I think what's missing in the level design for me are specific entry points / chokepoints for the enemies, so the player would have more decision-making when it came to how to place the turrets to be most effective. In fact if you were to introduce turret repositioning you could use the turret defence antlion level in Half Life 2 as a point of reference for this kind of more action-oriented take on the genre!