Impressive work by all the team. If this had been a 7 day jam it wouldn't have surprised me if this felt like an actual game that ( with a little polish) could be released.
Things I will mention should you decide there is any future in revisiting this project or using any of it's elements in your other games.
1. The main offender:
The most busted thing seems to be the speed boost on kills bonus. I don't think your camera controller script (or your cinemachine settings if you are using that) is designed to cope with the chaos that this can cause, the player almost "visually teleporting" from one side of the screen to the other as the camera struggles to keep up. I think this is a big part of why others were struggling to keep track of the player.
2. Balance and game issues:
Big problems, but this is not so much of a criticism as I know in the end you all didn't have time to finish it to how you wanted it to be. But if you were to revisit this or reuse them in another project you would really need to think of where to go with the project or how to (sanely) reuse some of the ideas.
3. It looks and sounds AMAZING! (This is a huge positive).
The aesthetic both visually and audio wise were both top notch. If you made a cohesive trailer for a game with this artstyle and stylistically similar music & fitting audio, it'd be an instant Steam wishlist for me. All that you'd need to complete the trinity there would be a fun and addictive game!
All in all I just wish you had had more time to accomplish what you wanted from the game. I hope all the ideas from it aren't just gonna be abandoned because they would have had a lot of potential in a jam with a more forgiving time constraint.