This is a good game even for adults. However, if you have any young children this is a great game. My 5 year old and 3 year old have logged 90 hours in this game since it released. The coop has a mechanic similar to the "bubble" in New Super Mario Bros Wii to help the young ones float behind older siblings if they get stuck. My daughter in particular burnt quite a bit of time playing in Kirby's house which works sort of like a dollhouse you furnish with the items you collect in the levels.
The only people I wouldn't really recommend the game for are your average 12-20 year old boys who believe they need "mature" content, but are still too immature to realize that a lot of "mature" content is actually pretty juvenile.