Kirby Epic Yarn is not my favorite Kirby game, and I prefer Good Feel's previous creation, Warioland Shake It, but I still enjoyed it.
It's the easiest thing in the world, but only to casual gamers. If you are an hardcore gamer and want to finish it getting 100% of the content, it can be very frustrating. To get the maximum rank in each level, you must do them without getting hit once, somethimes, and trust me, in some levels it's extremely hard!
It's definitely harder to 100% than its Wario counterpart, this for sure (I "100%d" both).
Anyway, my first Kirby game was Kirby's Adventure, and I fell in love with it because "it's like Super Mario Land 2 and Warioland, but you can also fly and copy abilities from enemies".
I still love that game and it's the only Sakurai directed Kirby game that I consider a real masterpiece (Dremland 1 is too short and it's just an experiment, Air Ride is a bit rough and too much achievement based, and Superstar is too much fighting and treasure hunt oriented for my tastes).
EDIT: Actually, I'm doing (on paper) a concept of a Kirby game that's a mix between Superstar and Dreamland 3/64, and it features a larger ability tree structured into levels; in the lower levels, abilities are simpler and your life gauge is splitted in 5 pieces (with no abilities, just 4), while higher level abilities are weaker, but have more complex movesets and the life gauge is splitted into more pieces so you can be hit more (example: Kirby is Lv1; Stone Kirby is Lv2 and can kill enemies with 1 hit; Fighter Kirby is Lv4 and needs 3 hits to kill an enemy, but it's a lot faster and has more defense). There are also some Lv0 abilities, like vapor (water + fire), sleep and photo (this is for an after game mission); those abilities are power-down. Riding an animal/veichle brings you to Lv5 (that's the maximum level possible, except for LvMAX that's only for invincible candy and final weapons), but you can't combine your abilities with the animals (they are meant to allow a sort of "copy ability" for the other characters in multiplayer, those character who can't copy abilities). I'm planning to put Kirby, MetaKnight, Adeleine and Bandana Dee as playable characters, with Dedede as fake final boss, that can be unlocked as playable only after the end of the game, but I want to make a creative concept for their gameplay first (I'm thinking of using Gooey, Daroach and Chef Kawasaki as well, but I fear that there would be too many playable characters... unless we make an 8 PLAYER Kirby game O_o).
EDIT2: it would be interesting to make Ninja a Lv0 ability (life gauge splitted into 2 pieces) but giving it overpowered moves... in other words, stealth gameplay XD