Awesome job! We actually made a similar timeline mechanic.
My favorite moments were when I finally figured out how to counter the boss's movements, come up with the perfect sequence of actions, then run the player at 2x speed and feel like a badass. I was hoping for a few more of these moments, but I felt like I was back at square one when the boss changed its movements. I was almost hoping to feel like I was in a timeloop movie Edge of Tomorrow, learning every attack through several grueling deaths only to chain together an insane combo to finally take it down.