It has a Mario Paint-esque music creator/editor! How did I not know that until yesterday, when I read this post over at tinycartridge.com?
Oh, and it's not just any music creator/editor--it's a Balloon Fight-themed music creator/editor, as evidenced in this YouTube clip:
WarioWare: D.I.Y. will hit store shelves in North America on either March 29 or May 31, by the way. (Although most sources say it'll be released on the former date, Amazon.com says it'll be released on the latter.)
See also: 'More evidence that WarioWare D.I.Y. is going to be awesomely magnificent'