It's been about a month since The Shattering was released, so if you still haven't read it yet, there is a warning that there will be some spoilers released in this review.
I normally don't read books that are based on the Warcraft or World of Warcraft universe. Mostly because I had no interest in it. Well, at Blizzcon a lot of people were picking up the Prelude to Cataclysm book. So a decision was made, and I also purchased it, thankfully on the first day, as it was sold out by the 2nd. I ended up reading it on the way back to the East Coast.
The book itself is situated around several different characters, Varian, Anduin, Garrosh, Thrall, Jaina, Cairne, Baine.. well..basically almost every "main" character in current World of Warcraft lore. It starts off with Drek'Thar (you know, the AV Boss), having a vision of the world crumbling, and then it starts right off with Cairne headed to Northrend to pick up the rest of the troops no longer needed there, and ready to return home. This is the first time you really see Garrosh as well, and seriously, they don't make him very likable. Chapter two begins with a fight against the Kvaldir, which interested me because I really didn't pay much attention to Lore in Northrend, especially against this new race of humanoids. Obviously the Horde defeat the Kvaldir, and return to Orgrimmar where there is a parade of sorts for the heroes.
Then you get switched to the Alliance side of things. Jaina Proudmoore is attending a service to remember the soldiers that fell in battle. They also delve a little into Varian's past, which if you're like me and don't follow Alliance lore too much, it was confusing a bit, cause I couldn't understand why Varian had "been split into two separate entities" , or really how it had been done outside of he had no memory of his past. You also meet Anduin here, and by the end of the book, he had become one of my favorite characters. He does grow quite a lot in this book, going from a small boy to nearly an adult. His father decides to allow him to visit Jaina Proudmoore in Theramore, and eventually he also goes to live with the Dwarves which end up with him kidnapped, but we'll get to that later. I should also note, that this book made me hate Varian a little less then I did prior. He's not all too bad a character, and I can now see why he has so much hatred for Orcs.
Eventually you get sent back to Thrall waking up to horns blasting in Orgrimmar, to find the city on fire. He attempts to control the elements, but they refuse to listen to him, which obviously worries the Shaman-Orc. It is shortly after this happens, that Thrall decides he must go visit Nagrand, and requests that Garrosh sits in his throne and watches over The Horde while Thrall is gone. This is currently happening in game, though a bit different then how it is figured. In the book, Thrall commands no one go with him (and therefore all those people at the Throne with him live in game right now, never happened in the game). He also has a small fight with Cairne Bloodhoof, the leader of the Tauren, about leaving Garrosh in charge. Cairne brings up a good point in his argument:
"They love him because they only see the glory! They do not see the foolishness. I, too, saw the glory. I saw tactics and wisdom, and perhaps with nurturing and guidance those are the seeds that will take root in Garrosh's soul. But he finds it far too easy to act without thinking, to ignore that inner wisdom. There are things about him I respect and admire, Thrall. Mistake me not. But he is not fit to lead the Horde, any more than Grom was." 
They then switch back over to the Alliance, where Anduin is now staying with Magni Bronzebeard in Ironforge. This is where Anduin really starts to grow as a character. He begins training with Lady Dwarf Aerin, who teaches him sparring and Ram Riding, but does become best friends with High Priest Rohan, as well as several dwarves from the Explorer's League. Eventually the Dwarves find a shattered tablet that is written of the earthen. It speaks of "becoming one with the earth", which then eventually leads the Dwarves to think that whoever does the ritual will be able to speak with the earth, this of course after several Earthquakes, that basically ruin Kharanos. Anduin pleads Aerin to take him to Kharanos so he may assist, and so they go. Eventually they send Aerin down into the distillery to retrieve people who are trapped, but another small quake breaks the inn even further, and in the process kills Aerin, which breaks Anduin's heart, due to the amount of time they had spent together, as well as the amount of trust and respect he had for her. Several days after the earthquake, the ritual is ready, and Magni has decided he will do the ritual himself to talk to the earth. Well of course things don't go as great as they should. The ritual actually meant "become one with the earth", and Magni is turned into a crystal, with nothing that can be done. The Dwarves are left leaderless, for the time being.
Part two is the most interesting of the book, where Thrall meets in Nagrand with Greatmother Geyah, and her apprentice of types, Aggra, who becomes Thrall's teacher, and later his, well, it never says mate, or girlfriend in the book, but the context is there. He asks her to return to Durotar with him, and she accepts, but this is near the end of the book. While Thrall is in Nagrand doing his Shamanistic duties, Anduin is stuck in Ironforge, held captive by none other then Moira Bronzebeard, Magni's daughter, and Dagran Thaurissan, her infant son, and a large group of Dark Irons, who have come to claim her throne to Ironforge. Ironforge is then shut down, no one out, no one in, ordered by Moira, of course, to keep people inside and so the outside world can not hear of the ongoings on the city.
A bunch of Night Elf and Tauren druids meet up to discuss the treaty and the attack upon Sentinels earlier in the book. However, there meeting is cut short by Twilight Hammer cultists, who kill all but thankfully leave Hamuul Runetotem slightly alive, and thus he is able to get word back to Cairne about the attack. Cairne is not too pleased, for the Cultists in their intelligence during the attack, leave Hamuul believing Garrosh requested this attack. So Cairne heads to Orgrimmar and has words with Garrosh, who is getting intricate tattoos upon his face. Eventually Cairne challenges Garrosh to a mak'gora, which is basically a fight to the death with no armor, and one weapon. The fight is written very well. It is here that Cairne falls to Garrosh because of the poison upon Garrosh's weapon, blessed by none other then Magatha, leader of the Grimtotems. The resulting coup of Thunder Bluff is probably my favorite part in the entirety of the book. Baine, Cairne's son escapes and flees to Jaina Proudmoore.
So at this point, to review, Moira is in charge of Ironforge, and Grimtotems are in charge of Thunder Bluff. Thrall is still in Nagrand about to do his Spirit Quest. Varian is about to lead an attack on Ironforge via the Deeprun Tram to obtain his son and kill Moira and her son. Anduin, Baine, and Jaina are speaking in Theramore (Anduin got there via use of a Hearthstone Jaina had given him previously in the book). I don't want to spoil the growth of Anduin and Baine at this point, because I really think people should read the book if not for this conversation between the two growing sons of two opposite Factions.
So eventually Baine recaptures Thunder Bluff, and Garrosh refuses assistance to Magatha and the Grimtotem after finding out what Magatha had done. Anduin returns to Ironforge, just in time to find his father leading an attack and about to kill Moira. Anduin has grown so much in this time, and gives his father advice that a King should be proud of, hearing from his only son:
"Then let her answer to the law, to her people, for what she has done to them. Father -- you're a king, a good one, one who wants to do the right thing. You believe in the law. In justice. You're not some--some vigilante. Destruction... Destruction is easy. Creating something good, something right, something that lasts--that's what's hard. It'd be easy to kill her. But you have to think of what's best for the people of Ironforge. For the dwarves--all of them. What is wrong with the dwarves' deciding how much or how little they want to participate in the world's politics? What's wrong with reaching out to the Dark Irons if they are amenable?" 
Varian then decides his son is correct, and instead tells her she must choose a representative from each clan, Dark Iron, Bronzebeard and Wildhammer, and she must listen to the representative. Varian then returns home with his son.
The book comes to a close, soon after. There is of course more delving into Thrall and his spirit quest, but I feel it's unnecessary for me to tell you every little thing that happens between Aggra and Thrall, and if you wish you may read it yourself. Thrall returns back to Azeroth, with Aggra at his side, a vision leads Thrall to believe that the wound started in the Maelstrom, and so Thrall and Aggra head there in the epilogue. Before they leave, Thrall gives his spot up to Garrosh, leaving him as the Warchief of the Horde.
The book also references the War of the Nightmare several times, so I suggest you familiarize yourself with this if you haven't already.
I should note that in the book, they don't fully mention a lot of cultist activity. It's sort of touched on a little bit, with attacks on Night Elves and Tauren Druids, but not really approached at a high level, as they did/are doing currently live in game.
Overall, I thought the book was really good, and give it an 8 out of 10.