It's a cool idea and the game looks very nice. It was really satisfying every time to release the barrage of bullets. The title screen / tutorial was great too and the game was easy to get into.
However, even with some enemy variety being introduced I never felt like the gameplay while charging really picked up. I think I'd have either liked to see more complex bullet patterns but also allowing the player to move during the charging, or just something else to do during the game like collecting power-ups.