Best 2D game EVER
It has everything you can want in a Kirby game with plenty of different powers to use and many different game modes (with co-op mode for nearly all of them). The gameplay itself never has any problems with perfect control.
Every mode has a bit of a different feel to it, from being cinematic to a normal Kirby game. Though all the different modes in it give you a great feeling of satisfaction when beaten (especially if you can find all the treasure).
If you want a good 2D game, don't get it when you can get the best 2D game in the form of Kirby. It's hard to find, but if you have it, it's totally worth the purchase.