Outside of the cooperative play, the new worlds, and new power-ups, the game really doesn't offer anything truly unique to the series. Nintendo made some creative choices, but basically played it safe, and who can blame them? When you have honed such a successful and solid formula, there's little reason to deviate too far from it. And New Super Mario Bros. Wii doesn't... but that doesn't mean it's not a must-have for Mario fans and Wii owners. It also easily ranks among the best in the series, certainly offering more challenge and content than New Super Mario Bros. DS.
Despite being feeling and looking somewhat familiar (which is definitely a positive in this case), New Super Mario Bros. Wii is one of your safest and best best on the Wii this year.