I've seen this book in play once in addition to play testing early versions of it. We were doing a Spell Jammer-esque game of DW for a goofy one shot that I was DMing. The Living Star (LS) was fun to watch. This class doesn't fit in a typical fantasy game, but if you are doing something more atypical it should be a welcomed addition. The core mechanic is seldom seen (I've only seen something like it in one other playbook, an ice mage of some sort) so it has a very unique feel compared to other classes. The player said he had fun with it and the class seemed to work just fine with the other classes in play (no toes were stepped on for the duration of the game). The LS can go many directions based on what you choose for your advanced moves which makes it a welcome addition to any group.
The only problem that crept up was when the group was trying to make camp every time the LS was low/out of Radiance. The LS player really wanted to avoid taking damage for recharging. I allowed it the first time but after that I made sure to not give the party that much down time to keep healing up. So just watch out for that.
Also the authors notes at the end explaining intent and extras are a definite bonus and I wish other play books would follow suit on moves that can be harder to interpret.
I'm giving this product a 5 star review because it is put together well (character sheet is clean and organized, the book is easy to read and the extras are fun) and the price is fair since it's around what most people charge for a single class, yet the LS offers a little extra with some author's notes and moves that weren't thrown in originally but were included if you wanted to use them.
[5 of 5 Stars!]