So no major spoilers ahead, indeed my review will be more of a comment on the Tau's and Xenos in general's fiction (or lack of), and the community opinions/response to this. Don't worry, I'll talk about the book too!
So what do you get for your £18.99 or regional equivalent?
A hardback, fairly large print novel of 355 pages by Phil Kelly (more on him later), centering on the eponymous hero's exploits crossing the Damocles Gulf and generally plot device-ing himself and his super awesome squad of justice and tolerance out of the various slightly sticky situations they find themselves in. Presumably there's more to come too, as we don't get any Enclave action at all; this is a prequel, or backstory of sorts.
That's the plot in a nutshell, without spoiling anything - there are subplots involving the Inquisition, an oddly-behaved member of the Water caste, the machinations of the Ethereal caste and the best efforts of the Scar Lords chapter to derail Farsight's expedition. Beyond that, we glean something here and there about Farsight's relationships with Commander Shadowsun, That Guy Kais and his old mentor Puretide, but nothing anyone with a basic grounding in Tau lore wouldn't be au fait with. (I'm not including myself in that group, as a Tau noob).
As for Commander Farsight himself, there's plenty of him getting slightly miffed and emotional about things not going the way he wants, presumably as a prelude to him having the eponymous crisis of faith (at some point). Whether you find it natural or too jarring with the traditional ideas of the Tau obediently going about their for the Greater Good business is largely down to you. His command team are blatantly OP though. One of them is basically a Dreadnought and another is a Cylon. Come at me, bro!
You also get a brief but useful Xenolexicon at the back, (although if I'm being uncharitable, it would've been nice had this been mentioned in a contents page, I only found it about a fifth of the way through my reading...)
This brings me onto a more general discussion - many of the Tau's hardcore fans have very strong feelings about Mr. Kelly, usually positive in regards to his original involvement with previous Tau codex fluff, and vehemently negative when it comes to his recent move into novel writing.
I'm as bad as anyone else when it comes to debating my favourite sci-fantasy universe, but the 'colour of Tau blood' debacle (alluded to in the recent Community post announcing the novel) and the somewhat shaky ground of the 'kind of make it up as you go along' Tau language are problems laid at Phil Kelly's feet. As a Tau noob, these things don't bother me unduly, but I know instinctively that they probably would be doing if I'd had a longer relationship with the little blue guys.
On a wider scale, these issues are felt more by a fan base when that group is smaller; write a bad Space Marine novel and enough people will buy it and/or think it's half-decent, and encourage the company to publish more - write a 'bad' Xenos novel and the relatively few people who buy it will desperately wish for it to be good and be all the more enraged when it's not, usually leading to no further novels for that particular faction for a while. It's a vicious circle but hey, newsflash, Marine stuff is popular, sells well, and thusly gets more stuff published for it.