This is a pretty well thought out and balanced book with enough options to make pretty much any kind of kineticist you want. The risk reward of accepting burn in this book is much MUCH better, it's still punishing but doesn't make your character useless. Which this is the biggest issue the kineticist had in 1e. Before going too deep this is definetly worth double the price they are asking. There are just a few issues.
As with many releases this does have a number of typos, and the electricity kineticist is absent from the elemental defense feature at level 17, I assumed that following the pattern set by the other elements it is an upgrade from the 5th level elemental defense bringing reflex to legendary. Otherwise the typos aren't too distracting, and are easy to understand what was meant.
There are two main balancing issues that I can see, the extended range (1st level), and extreme range(4th level) feel a bit too low level, extended range changes your blasts from a range of 30ft to a range of 120ft or 300ft with air blast, extreme gives you 500ft or 1000ft with air blast. Those are very big jumps for such a low level requirement. I would add one more range feat to set it at 60ft, start the feat tree at 4th level, 8th level, 12th level.
The other balancing issue I can see, which is both a small and big one, is Kinetic Revivification (14th level), when you heal a creature with kinetic healing you remove their wounded value. This is very powerful, though you need to go down the specific choices to get there, and you can only cast kinetic healing so many times as a focus spell. Having it lower the wounded value by 1 or 2 would be fine or having the target be bolstered to the effect for 24 hours would balance it out, but completely removing it messes with the threat of death in your game. I know this won't be seen as an issue in everyone's gaming group, but I'm just putting it out there.
My last and final issue is that all but one of the highest tier of infusions are for fire and force, the only other one being aether, air, water. There isn't one for all of the types, and there are 4 or 5 elements that just don't get one at the highest tier. Now there are still a huge selection of infusions, but I am just a bit disappointed that the last set you get which only has 4 options is pretty much just for fire and force. I understand that most people will play a pyro, but I like making electrokineticists and cryokineticists. This is just a minor gripe though.
As for what I loved, the options really play into the feel of the elements, with a class feat for each element a few general class feats and some mixed element feats for every level. There are multiple ways to do the same thing with different elements so you almost never feel locked out of a certain kind of build based on your element. The capstones feel like capstones, with things like using your lightning to teleport to anywhere you can see by transforming yourself into a lightning bolt, or creating a tidal wave hitting all creatures near a shoreline 5 miles wide and 1 mile inland with your water blast damage or you can just flood the area over 10 minutes and deal no damage if you want.
This is an excellent product, and I am very excited to incorporate it into my gaming group, I know I didn't gush over it as much as it deserves, but it's a big book and I complained about maybe one page worth of things.