Too easy...but then again so is Super Mario World, and we all love that
I actually had a hard time putting it down. It took me two days to plow through on the fact that it was both easy and downright FUN. Kasa (or Perry) is a great addition that gives a much needed melee attack to the 2D series ever since first introduced in Mario 64. The story is a laughable joke, and I found myself skipping the cutscenes with the ever useful B-Button so I could get back to the gameplay.
A few new elements kinda detract from the original game. Peach simply has TOO MANY hearts, but I'm kinda glad she had them while I played through a few of the boss fights which could be surprisingly tough at times. And I also heard a few complaints about the level designs and how they are so "not Mario-ish." This is VERY true. I don't think that the Mario level designers worked on this, but rather the Kirby level designers. I felt immersed in the world of Kirby's Adventure rather than the Mushroom Kingdom wannabe island. While definitely falling short of the masterful levels of SMB3, they work for this game.
Also the game is pretty sexist how Peach's ultimate power is to lose control of her emotions...but I think it's pretty damn funny
The new elements thrown into the mix add a new sense of fun, and I am looking forward to the next Peach game if they make one.