I didn't really feel I needed the time shift to get to the boss with plenty of health (though I still didn't manage to beat him, only got him down to 33% health). The 2 second cooldown on it felt really not great, so I didn't use it. I think it's not very intuitive for it to have a cooldown yet be represented by a bar that doesn't communicate that in any way.
There's some bugs, like the doors blocking bullets even after they go away, and in general hitboxes don't feel super precise. I love this genre though and always have a good time playing it and this was no exception!