A great game with minor set backs...
This concept is completely original. I've never played a game like this before. *Big-thumbs-up* But I feel that the difficulty progressed too quickly. I think a primary problem is that the character moves slower than the enemies can shoot their weapons. The lack of speed does pose the biggest problem, because even though you're invulnerable while carrying the cubes you are still limited to the amount of time to shoot it before it disappears.
You did forewarn us in the "Author's Comments" that there would be a lack of weapon upgrades and boss battles so I can't be too mad about that. But you did include power-ups. These were a big help. I was disappointed that if you died once you were prompted to return to the menu- not a single retry. This takes away from the fun factor and the replay value.
Overall, the game is one of a kind and challenging. The music was very fitting, as well. I look forward to more.