Very cool!
The action is fast-paced, the grpahics are good, and the controls are responsive. I also like that you can jump between edges of the screen--that's a fun tactical ability to have. I also like that you don't "die"--you just lose points from being hit by the enemies.
My one complaint: it's hard as all hell to see where you are when you're moving around because of all those "expanding ring of water" effects, and doubly so when you're moving and firing off a stream of shots. I found myself totally unable to locate my character on more than a couple of occasions. Fix that, and this will be the perfect time-waster. :-)