Awesome music, beautiful pixel art, and really fun and unique gameplay (I love the idea of having spinning arenas!) make for an excellent game.

This is certainly a game.

The gameplay is kind of repetitive, and a lack of scoring system combined with what seems to be completely flat difficulty means that there's not much to keep people playing for more than a few minutes. Perhaps you could add stuff like powerups (for example, a shield to protect the player from a hit or an upgrade that makes them fire spread shots)?