Really cool game! It took a while to realise how important the rolling was (though you did point that out in the instructions!), and once I started using it more, the game got a lot more fun. The power-up coming based on the dice you get when you roll is a really smart mechanic, because it encourages the gameplay you want -- having them roll and swap weapons constantly. Very cool.
I'll mention though that you probably want the next wave delay to end (or at least shorten) once all the enemies in the current wave is done, otherwise the player is just standing around, waiting for the enemies to appear. (Also, the grey on grey was a bit hard to see; some more contrast between the player and the background would have been nice, though the enemies were all very visible!)