The combat in this game is very satisfying and the art is very charming, but I never found a reason to use the time freeze mechanic (which looks very cool, btw). Since enemies all die in one hit and you can pierce infinitely, you can just clear enemies indefinitely by spam firing. Making the enemies faster over time (or making the enemy speed ramp up faster, if you did already) may help necessitate the use of time freezing.
Also, is it just me or does the music slider not work? I was messing with the sound settings and while the SFX changed like it was supposed to, I didn't notice a difference in the BGM. Perhaps your range is too small?