Good core, my gripe was with the collisions with the walls. The walls and pillars aren't transparent, and things, me included, would "hide" behind them which felt glitchy. Sometimes I'd get stuck around looking for a pick-up. It often felt like the momentum of play was often interrupted. Perhaps let the player keep some of their momentum after bouncing off, or redirecting it in some way, or maybe even increasing the damage and accelerating if the player deals a killing blow, to line up an awesome shot.
A lot to do with this concept, and the effects were really good!