The concept is really cool. Sometimes it doesn't fire next to walls and i think it would play much smoother if the die would accelerate a little faster and you could stop faster by pressing space bar. The enemies sometimes pop in form the screen border with a lot of speed already. If you see them late it is really hard to dodge.
I think the reload mechanic is really nice! You have to pay attention to the die and can manipulate how many shots you fire really well if you know the opposing faces.
Last thing is i wish you had some direction indicators for enemies that are not in range. Level 3 takes a while to complete because you have to search for enemies.
Overall a great game! I really like the visuals.