If you're someone who loves a real "elemental" or "telekinetic" type character, this book is something you will absolutely love. The Kineticist is the sort of character class people have been wishing for since the dawn of such games. While the rest of the book is "meh", the Kineticist makes this book worth the purchase. I find the theme and mechanics of it to far exceed 3rd-party attempts to do something similar, in no small part due to the fact that glaring new rules are more acceptable if they come from Paizo.
I'm of the assumption that the low scores on this book are people who don't belong to the Kineticist mindset. The mechanics on the kineticist are very unique to Pathfinder, and unlike any other class (whereas all the other classes in the book strongly mirror what you'd imagine an archetype of another class might look like). At first look, it likely seems a mechanical disaster due to your mechanical strength also being your mechanical weakness, but in-play the class meshes very well together.