Just 100%'ed my file. I really enjoyed the game, but have some criticisms of it too.
As a single player experience I enjoyed Epic Yarn more. Which is weird because Epic Yarn's first few levels were such a turn off for me that it took me years to finally pick it up. The stages in the game are roughly the same difficulty if you're trying for all the treasures / gold bead count in Epic Yarn, or gears in this game. Which is to say, minimal challenges on all, but a few stages. The four, or five stages I had to play more than once were usually because I had to learn what I needed in a specific room, rather than an actual platform challenge. It's a shame the tougher mode that's unlocked when beating the game wasn't available from the start.
That said, I was really happy with the Challenge Rooms. Are these the sorts of extra stages that are coming on the Kirby Collection disc? If so, that'll be amazing. Getting Gold after an hour of perfecting a room is very satisfying.
Maybe the most fun I had though was the short time I had playing multiplayer with two other people though. Like NSMB Wii, I think this is a game that really benefits from having people to play with. I don't think the level design is quite as uniquely tailored to the game as NSMB Wii, but you run into a lot of similar situations where you're all racing for a power up, stars, grabbing each other, etc. Very fun and I look forward to play the tougher mode with more people.