Split between the single and multiplayer - yes, it has multiplayer.
http://www.nintendoworldreport.com/news/75972/rhythm-heaven-groove-to-feature-over-100-minigames
Rhythm Heaven Groove is not lacking in content, as confirmed in today's Nintendo Direct.
The opening game of the show showed an extended gameplay trailer for the July 2 release, and confirmed there would be more than 80 single player minigames and more than 30 multiplayer ones (up to 4 players).
Other modes of play, including an RPG-like mode called "Beatspell", also appeared.
