Part 1 can be found here covering the book's rules
Even in comparison to 40K's many races, the Tau Empire is insanely easy to screw up. Yes, getting the Craftworld Eldar down without making them too human and keeping a degree of mystery is surprisingly difficult. As is writing space marines without allowing for favoritism to overwhelm writing direction and keeping each chapter equal and uniquely interesting. The same goes with the Imperial Guard, presenting them as a competent force who dies due to the sheer power of those they fight than Zapp Brannigan tactics. However the tau have the unique problem of having two very separate interpretations, both of which have to be balance without one overwhelming the other.
On the one side the tau have the idea that they are the last, best hope for a good galaxy much like the Emperor of Mankind's great crusade was. Uniting all races under a single banner without the need for the relentless conflict which has dominated the galaxy for millennia. However, going too far with this and bringing them up as having no dark side can easily alienate them from the universe or make them seem like a overwhelmingly perfect faction.
To balance this out later editions added hints of their society being an Orwellian dictatorship with mind control, eugenics and propaganda disguising its true nature. The problem is that this was always intended to be shown through hints and potential suggestions, as if the lore in the book was propaganda. In many recent books this latter point has been overwhelmingly prevalent, and turns the Tau Empire from an interesting mystery into a dull "lol 1984" force without depth. This problem continues here and strangles any and all mystery, interest or balance which had been so carefully built up surrounding the tau.
Let this be made absolutely clear: What is written here isn't made as opinion or misinterpretation of events. There are no obviously biased accounts, no flavoured text which contradicts the events of Codex: Tau Empire or even a suggestion Farsight himself might be being manipulated by his alien weapon. No, instead everything is rammed down the reader's throat as absolute unquestionable fact and leaves no room for interpretation. The Ethereals are evil manipulators who care nothing for their subjects, the Tau Empire is a complete dystopia thirsting for control over others, mind control is rife, free will and independence are completely opposed. There is no grey to them, only black to oppose Farsight's white morality.
Farsight Enclaves makes the point of turning many elements and ideas introduced from Tau Empire and promptly altering details to turn them into examples of how corrupt the Ethereals really are. Things like the Puretide Neurochips, which imbue his teachings onto commanders implanted with them, are made to kill their users if anyone tries to remove them. The Ethereals themselves are now stated to be stamping out all knowledge of the Warp, psychics or even any hint of truth about Chaos, not to mention heavily manipulating and sacrificing the lives of their citizens if need be.
Some new details make a weird kind of sense but only if you ignore half the established facts. For example, the new idea that the Ethereals intentionally provoked the Imperium into launching the Damocles Crusade quickly, so they wouldn't gather up a bigger force to kill them. This feels like the sort of decision the Ethereals would make to ensure the Empire's survival, but ignores half the facts behind them. Like the fact the Ethereals know little of the Imperium's actual size or power, that they had never met a full Imperial force to gauge their strength and that they made no obvious efforts to prepare for the conflict.
The same goes for the above examples of the Puretide Neurochips (Farsight tried to remove them as Puretide had never known about the existance psykers and his tactics wouldn't work) and the Ethereals' suppression of all knowledge of the Warp. The book completely and utterly ignores that the Empire has run into psykers multiple times and EVEN HAS WARP SENSITIVE RACES ALLIED TO THEM!
The orks, who are all latently psychic and have ones they will use in offensive operations? Completely ignores them. The kroot who ate their flesh and gained their powers? Pretends they don't exist. The highly psychic nicassar who are not only a member race but serve as military auxiliaries? The book treats them like non-persons whenever these points are brought up. Even events like the war against Tark'ax are treated as if they never happened and completely ignore the presentation of Ethereals there.
The book ultimately took the Brian Bendis approach to writing: come up with an objective you want, then bulldoze your way to it via the most direct means. If something contradicts you or might cause you problems, either kill it off or pretend it never happened. That's really the issue here as it only keeps the bits the writers wanted, but any bits which were contradictory or were at odds with what was suggested were ditched entirely. They wanted the Tau Empire to be a horrible dystopia, for Farsight to be a heroic rebellion acting against them, and went about it without bothering to have it make any actual sense. Now, in fairness ignoring this practice you can see some talent behind Farsight's personal story and development. It's not too bad as things go and there is a logical progression behind his eventual rebellion against the Empire. The problem is that it came at not only the cost of the canon and the Tau Empire's ambiguity in its nature, but also Farsight's more interesting qualities.
The thing which made Farsight so interesting was the lack of details behind just why he actually turned. The events on Arthas Moloch, the effect the death of all Ethereals in his expedition (not to mention the nature of their deaths), his abnormally long life, and most of all the origin and nature of the Dawn Blade. All of these were aspects we only knew fragmented hints of information behind and led to a multitude of fan theories, each working off of the scraps and details we were given. Theories surrounding the Blade ranged from it controlling Farsight, to it being one of the lost eldar blades of Vaul, being of daemonic origin or even a C'tan weapon. All of these were crushed in the single most disappointing way possible.
The origin of the Dawn Blade is that it comes from a random long dead race with some Warp knowledge. Their name is never mentioned but it's clear they have no connection to the necrons, eldar, daemons or even the most insane of theories. Their items are not corrupt, only that they knew of the Warp, and Farsight's encounter only does the bare minimum with the experience on the world. Its origins are never gone into, its people never explored, no tantalising hints are dropped, nothing is done with it beyond getting Farsight to know of daemons and giving his army items. They don't even bother to do something as basic as declare it the dead world of the Interax and latch onto the success of Horus Rising. Ten years of speculations, fan theories and attention built up from a lack of knowledge, and the writers make no effort to give it a good payoff.
Even the Dawn Blade itself and Farsight's longevity is explored and detailed in the most insultingly dull manner imaginable. The Dawn Blade is made of life draining metal, and has turned Farsight into a vampire. The codex delivers this with about as much mystery, information and immersion as that sentence. It makes no effort to try and have the reader buy into it, feel like a compelling character aspect or even try to have Farsight react to its effects claiming he knows nothing of its nature. Even by 40K's standards, its effects make no real sense as they are not explained and do not play off of long established supernatural means like the Warp. Worse still, this lack of explanation or reasoning spreads to the rest of the book.
They have clearly been created to give Farsight's forces some flavour, but have no semblance of logic behind them. Why do they exist? Just because. Why did the tau settle on these worlds rather than better suited ones? Just because. Why did they do half the things they did to them and not properly terraform them? Just because. Like so much here they only work and seem interesting when you are actively not thinking about what has been written down.
It was stated in the rules section of this review that it felt as if this supplement had been rushed. That the writers had been forced to churn this out in a couple of weeks to meet a deadline and as a result it felt uninspired. Going from this fluff, they were not only rushed but were lazy when it came to writing. There is no effort here which has been put into making sense or event taking advantage of the goldmine of opportunities present in this book. It feels as if it was farted out in mere minutes and written even as people were thinking up ideas. Combined the massive typos and recycled artwork, yes they did this again, it's not a hard thing to consider of the book.
Iyanden was a disaster, a trainwreck of a codex which openly shat upon everything within its pages. It was insultingly badly written, mocked all within and was the worst book made in the hobby's twenty years. The Farsight Enclaves feels boring, badly researched, rushed and is only just better than the prior supplement thanks to a lack of "invisible sky wizard" levels of insanity. A scant few of the rules work, but the majority do not and the fluff utterly fails in so many areas it might as well have removed itself from the canon.
The only area that the book can really be praised for is the profiles of its characters. Nearly all of the Eight have very interesting backgrounds ranging from a mad scientist tau commanding a Riptide to a full blown sentient AI operating with Farsight's forces. Each has interesting details to them as at the bare minimum are passable. The problem is that they're not very well integrated into the stories beyond their individual profiles, making this lone example of quality isolated within the book.
If you desperately want an all battlesuit army for the Tau Empire, you might want to pick this one up. Otherwise, give it a miss. You'll only save yourself a lot of money and a lot of pain.