Basically just a (nice) tech demo.
With lower-speed songs the gameplay is really only as much fun as the music. It would benefit from more complexity. Powerups, or maybe sometimes you have to dodge objects rather than catch them. An excuse to slap the spacebar now and again would be nice, maybe in service of Ikaruga-style polarity switching?
At higher speeds the game is unplayable. Whenever the stream switches direction (clockwise to counter-clockwise or vice-versa) your life drains to zero before you even realize what's happening. There are two solutions. One, you just accept that higher songs are more difficult and that you have to train on slower songs, and work your way up. This would be okay if slower songs were fun enough to make practicing on them fun. The other would be to find some balancing mechanic to separate difficulty from tempo - for instance, missing a beat could cost you less life on higher-tempo songs.
Also needs a pause button and a mute button for the main menu.