The roll mechanic is excellent.
I like how both the physical rolling of the die and changing of the die face are made into mechanics. Sometimes I didn't want to change my weapon but needed to roll to get out of a tight spot. Maybe with even higher diversity in weapons, the tradeoff of rolling could be even more interesting!
The starting difficulty was too hard (for me who doesn't play bullet hell games) so it made it a little difficult for me to experiment with the mechanics.