It's a really intense game, and it feels quite well balanced. Got the collectables for all but the one before last stage... I could barely complete that one normally :P
There were some stages where I had problems seeing the bullets, since they are the same color as the enemies, and there were a lot of splashes on the ground already.
Another piece of feedback would be to maybe reduce the camera zooms and shakes, since especially right after starting it made me a bit dizzy. Since before I start it starts zoomed out, and when I die it zooms out again. If I die quickly into a level, then it starts being nauseating for me...
The camera shake was otherwise pretty good, I especially like how the minigun had such strong camera shake that it was hard to see and aim. And that I would say represents handling a minigun quite well.
Overall a really polished game, had a ton of fun with it!