I really likes the saturated colors and how they contrast from the black background as well as the smooth lighting.
The sound effects of the enemies getting hit and the particle effects that come off of them makes them so satisfying to kill. I also like how the particles match the enemies, it makes it look like you're blasting chunks off of them.
I also liked how the game had different enemies to fight, though I was kind of hoping they would have more specialized attacks rather than having more health or shooting slightly faster. Perhaps you could have the enemies carry different weapon times, such as a shotgun that shoots a spread of bullets, a sniper whose bullet velocity is lightning fast, or a melee enemy that constantly runs towards you with a spiked bat.
I felt like the jumping wasn't that responsive whenever the cube was on a ramp or when the cube was standing on its corner. If the cube's rotation was meant to be a movement style choice, then perhaps a raycast boxcast that doesn't rotate can be used to determine if the box is grounded or not.
The jumping also felt kind of floaty, which made it frustrating to dodge bullets since my character would be stuck floating in the air while an undodgeable projectile would come towards me. I would suggest looking at the video, Better Jumping in Unity With Four Lines of Code. It really helped me understand how jumping in classic platformer games (such as Super Mario Bros) is satisfying and how to easily design the mechanic in Unity.
The rewind feature feels more of a secondary feature rather than the main ability of the game. Perhaps if there were more areas that required the rewind feature then it would feel much more useful. However, even if it's more of a secondary ability, it's still a REALLY cool effect watching everything travel backwards in time.