Best entry I've played so far! Loved pretty much everything about it, you took full advantage of your concept by executing it really well! A couple of feedback, hope you haven't already received:
• I would've loved a little "presentation" of the level, just to make sure I know where the various rocks and enemies are, and how many of them there are, before the die starts rolling (which covers a lot of the scene)
• There's no way to know how farther can the bullets go in advance. There's the feedback on the mouse (appreciated) to know if the bullet hits or not, but other than that, there's really no way to know in advance if you'll be able to hit the enemies or not. If you plan on expanding the game, it might be worth it to tell the player how far can the bullets go.
• The damage output of the enemies is very random, sometimes they deal 2 damage to you, sometimes they kill at half health. It was a bit offputting and sometimes killed me out of nowhere.
Other than these couple of things I noticed, I really can't say much. It was an excellent time, loved the vibe, the gameplay was great and incorporated very well the concept. You should be proud! Amazing job! :D