Much of what I am about to say has already been said by others.
Really like the art style of this one(as someone say: very CAVE-like)
The time rewind mechanic is pretty good and help with scoring but sometimes i been killed multiple times just because the rewind leave me in very close of a bullet.
As you said the rewind isn't very useful for players who don't care about scoring or strugglle to survive so you probably need to add another benefice when using it.
But it's a awesome game anyway with great potencial.
I wish you luck with the project :)