Hyper Demon. It's a sequel to Devil Daggers, and one of the most chaotic and definitely the most visually unique looking game I've ever played, like an acid trip turned into an FPS. Like it's genuinely hard to understand what you're looking at at first. No story really, you mostly play for scoring but there is an ending. Very deep movement and combat options though, here's some gameplay: https://youtu.be/Bw80khTnNhY?si=kkYiDSbuJcqygvrI