Underrated due to Canvas Curse
The most common 'flaw' associated with this game is it's failure to deviate from the norm for Kirby games. But I say, why fix what's not broken? I've played 4 or 5 kirby games and I've loved every minute. This game takes what I love and tweaks it in a number of places to make it that much better. Collecting chests is great knowing you'll get a tangible reward like a secret level or recolour of kirby for it. The graphics are also a high point for me. Rather than going for a 2 1/2-D look, Nintendo chose to sticks with nice sprites, updating them to look crisper and more lively.
I think this game recieved harsher than normal criticism because people are comparing it to canvas curse, which brought something entirely new to the table. All I'll say about that is that a great game remains great no matter what the competition.
Why did I only give it 8.5? It does have a few flaws. 1) It's a little short. even going back and getting all the chests, which is incredibly fun, shouldn't take more than 13 hours, and it could easily take less depending on your skill level. Also, it is very easy. I've listed it as 'easy' because getting all the chests does pose a challenge.
I highly recommend this game.