Good for traveling.
However, there are a few drawbacks:
There's an extremely annoying loading screen that pops up while you're playing. This happens to me at least 4-5 times per level, and without warning. Plus, the clock's still ticking while the screen is up, so this stupid screen is eating into your score...
Also - you have little control over which level you play next, and they all begin to look the same very quickly....
All in all, I had very low expectations, so it was easy to be pleased. I played heavily for a couple of weeks to pass the time while traveling, but haven't picked it up since.