I like how this game gave control of the antagonist to the players to create a pvp scenario. It's definitely a unique take on implementing pvp, especially with the scale and premise your team went for.
I think that the thing that could be improved, or I guess potentially could be revised are the level layouts. With how the characters function and shoot there could be unfair situations that could emerge from tactics like stalling and cornering, especially since the boss can freely move around the screen. This would require a lot of playtesting though so it would take a bit to properly test and implement changes this big.