While I enjoyed Super Mario Bros. Wii and its multiplayer mode, this one lets you work a lot more co-operatively between players (in general there's less pushing other characters into bottomless pits!). Each character (Kirby, Meta-Knight, King Dedede and Waddle Dee) has their own moves which it's fun to explore playing. If you're playing as a single player, however, your only option is to play as Kirby. The worlds are bright and beautiful, keeping to the traditional Kirby artstyle but bringing it to life in 3D.
A one player experience is enjoyable on its own, but it's really in multiplayer that this game shines. The levels are relatively easy, though there is room for replayability in collecting all the items from the levels you may not have found in your first run through. The normal level play might have been a little monotonous if not for the addition of challenges and mini games which unlock as you collect the gears in each level. These as easy to play and tough to master; getting a bronze medal is simple enough but gold requires some real skill and practice!
Progressing through the levels and gathering gears also unlocks multi-player games which add extra fun for those playing with friends, and another way to mix up the gameplay and add variety.
While its cute characters, bright graphics and cartoon style will definitely appeal to younger gamers, this game is just as fun for adult Kirby fans and even gamers new to the series. Older gamers familiar with the platform game genre will probably find the main game relatively easy, but still have to put a lot of work in to complete challenges and perhaps some harder levels.
(I've only completed the first two worlds, so my impression is based on these. If this game follows the traditional formula, later levels will be more difficult than the first few are. :) )