First of all, the artwork AMAZING, the feel of the game is so fun, fast paced and the music fits perfectly! Slow time effect was very well done and loved the fact that the enemies are the ones being slowed and you can shoot faster, but at the same time that the timestop is really limited which is good, so you can't just walk past the level on slowed time!
Loved the fact that enemies might have a gun or not, it felt randomised and so good!
Few points I think would make this game from amazing to Munching AMAZING:
1) More guns for sure, (I didn't get the other gun at all, maybe I didn't make it far enough), but in a game like this, it would be easy to introduce different guns, enemies dropping them and you could pick a new one up and the old one would disappear, so people could try different guns and settle on the one they like (Obviously need to make sure all the weapons are somewhat balanced, more powerful weapons are slower/etc.)
2) Enemies were a bit stupid :D If you stand far enough, so that they don't notice you but they're on the screen you could just shoot them. Maybe include a code of something like IF (tookDamage== true) { Attack/Shoot() }
3) I reaaaallly didn't like the mouse/crosshair being stuck on around you, felt like I'm restricted, love the aim, but give it freedom, it wouldn't make things any harder, since the bullet would have the same trajectory wouldn't it ? :)
4) Less ammo for sure, in the end I didn't even look at the ammo anymore, since I had more than 400 and could just pretty much keep shooting the whole time, melee was only used in the first two attack before I got the gun. I would love if you ran out of ammo every now and then if you didn't play smart and then you would have to take a risk on melee attack. Also maybe just a tad more health dropped, I found like 2 in the whole game and I went through multiple levels :D
5) Not sure about the camera movement, first I thought it was bad but then once I got used to it, it felt alright, maybe just some polishing on that. Also the TAB button on computer for timestop was in a bit of a weird place, but in the end since the time power was limited it didn't really matter that much, so wouldn't worry about that.
All that being said, this game is 5/5 on every aspect anyway, but this I could easily see on Steam being sold for like 5-10$ and raking in good money if you polish it a bit more and add bunch of levels and maybe create some kind of story as well to make the player feel a bit more progress in between levels!