Good, but has technical issues
I experienced a little bit of lagging, which by itself would not have been a problem. However, it seems to me that, when the game slows down, the enemies move more slowly but their rate of fire does not change, which results in the level getting filled up with bullets. After dying about 20 times somewhere around level 7, I reduced the quality to low and turned off the music, and suddenly the difficulty went from just plain unbeatable to too easy. That's probably the reason the other reviewers cannot agree about how difficult this game is.
Appart from that, I found this game really well made. The only other thing I didn't like was the controls. I always prefer keyboard controls for shmups, though that might be just me.