So much juice! I'm getting Hotline Miami vibes. Good work with the overall polish.
I have mixed feelings about slow motion as a core mechanic. Sometimes it feels like the optimal way to play (go slow) isn't the fun way to play (go fast). You can probably work around this by tweaking how the baby bar works, or how many enemies appear at once in later waves. I found that most of my deaths came from careless mistakes where I just wanted to go fast and shoot things.
But, I can see why slow-mo makes sense if the game turns into bullet hell later on with huge rooms of enemies. It's just a matter of balance.