Average and dull. Needs some work.
Starting off, this game can be extremely annoying. The controls have a hard learning slope that you won't learn unless you bother going longer into the game, which most people probably wouldn't. The fact that the game does have a visual type of "tutorial" on each stage select screen, which does help with the basic stuff.
There's only two game modes, however they're extremely short. They do have a good, smooth mix of getting harder and harder each stage, but like I said before, the controls make you not get as far.
The art isn't bad, but it's what I've seen from most of the stuff that goes through the portal and isn't exactly the best. If you fix up the controls and graphics, as well as add in a few more features, I'm sure the game would be significantly better.