The core idea here is very fun and uses the theme nicely, however in practice I found it to have a few issues firstly the difficulty scaling feels a bit too spongy with more enemies that offer pretty much the same level of challenge. A greater variety of enemies would have been nice to see. Additionally the player doesn't scale accordingly meaning inevitably you will either settle for a low roll or break 21. Getting over the limit is basically a guaranteed loss, some way to better fight against the odds would be encouraging as it feels like one mistakenly greedy roll of the dice and its over. When you do start over the lack of 'juice' with the menu buttons can have it being a bit of a slog back to square one.
I know that's a dense ramble of nitpicky feedback but I hope you understand I only have so much to say on account of the fact that I enjoyed your game! the presentation is cohesive and the core mechanics of the ammo/shooting system are very satisfying. This as great potential for iteration, great work!