The game was surely really well done on the graphical side of things. The enemies and the player ship are okay, but what shined the most to me were the UI and the parallax background, those were really great.
Aside from the eye candy stuff, the game itself is, in my opinion, not that fun. The enemies don't feel different and the powerups are not incisive enough. The gameplay itself doesn't really take anything from the "rewind" theme, which can be okay of course, but I personally prefer when core mechanics of game jam games revolve around the given theme.
The main thing that is lacking and that contributes greatly to draw back the fun in my opinion is the almost total lack of shooting feedback. This kind of games are entirely revolving around moving and shooting, so a lot of care must be put into those, to make them feel as rewarding as possible. Shooting an enemy feels like I'm shooting a wall, so something like screenshakes effect, blinking sprites, more evident animation etc. would have greatly helped the feel of the game. I also didn't really understand what was the point of using the mouse to shoot (with a custom pointer too), when there's no possibility to aim to shoot. I kept going back to the description of the game since I thought that I was missing something. It felt very counterintuitive.
On a smaller note, I also discovered that by staying on the top left corner of the screen you can cheese the whole game, except for the final boss of course.
I understand that you couldn't spend much time actually tinkering the game in Unity and I didn't intend to be mean or anything of course, I just wanted to give honest feedbacks. Given the situation, you've managed to obtain really nice results nonetheless, great job!