I think it'd be a good idea to add the slow-mo, I know you talked about it in the video, but it would still be such a cool thing for me and a lot of other people, maybe even better then time stop.
I know the game is early, and it's probably not gonna be the type of game I'm describing but if you added these, you'd basically get a sandbox mode which I think would be very fun if you wanna just mess around with enemies and feel really overpowered. I also think you should have infinite ammo and time stop/slow-mo in sandbox.
I also think it'd be a good idea to add a menu that lets you tinker with spawn rates, enemy health, etc. It would be really cool if an option in the menu for spawn rates was "Conveyor belt" which feeds you a single enemy of your choosing each time the last dies, or you can set it to auto and it will spawn a random/specific type of enemy.
And maybe a level builder would be really cool too! :O
I really like playing it even as it's not finished despite all the things I just said though!
Honestly I just wanna mess around Experiment with the weapons and mobs.