Nice game ! The visuals are pretty basic but works well. Though having some animated models would go a long way to make it more engaging. The color palette is ok and make it all looks pretty coherent.
Loved the dice rotation animation ! It's very trippy :)
In terms of gameplay, I pretty much agree with what has been said bellow and don't see much to add to that so I'll jut highlight some of them that seemed the most important for me.
A timer to indicate when the dice will rotate & maybe a way to impact it (lower or higher it if you kill a certain number of ennemies)
A higher fire rate on the default gun to keep up with the spawn rate. maybe lower the spawn rate a bit on the high value dice faces to avoid being overwhelmed too fast. And maybe a dash/dodge to get you out of tight situations ?
I encountered a small bug on the web version. when starting the game in full screen it seem to loop on something and the scene doesnt start I managed to go around that bug by leaving full screen and putting it bck when the fight start.
All in all It's a neat jam entry. The screenshake and particle effects definetly add some juice to it. good job :)