Spent the last four hours playing. I've actually spent a lot of time in the single-player mode. As others have said, it's got a very Super Mario Galaxy feel to it, and I agree. Multiplayer was challenging, especially since I started playing at midnight at level 1, only to come up against level 12-15 Japanese players. Hopefully things'll balance out in the near future.
Almost couldn't get myself to stop playing! "Just one more level..."