I doubt there'll be any new characters other than Luigi and Yoshi. Otherwise, there would be no "hook" or "surprise" for the next iteration of Super Mario Galaxy.

Single-player gaming is decent on the Wii, but it excels at multiplayer gaming madness! Wii bowling + friends + beer = total fun!

Also, the ability to download classic Nintendo and non-Nintendo game is pretty cool. I think it makes a worth investment.