In a nutshell, the book is best used as a door stop. The original Warcraft RPG had soo much potential, but its mechanic execution was awful. The WoW RPG follows in its predecessors footsteps. There may seem to be a lot of anger in this review. It is not anger, but frustration with how such a great setting could be messed up so royally.
I'll go pretty much chapter by chapter in my rant:
Chapter 1: Abilities
Renaming attributes is probably the #1 mistake in this book. It makes it a hassle when trying to use WoW material in a non-WoW setting, or when trying to import non-WoW material into WoW.
Chapter 2: Races
While the inclusion of racial levels was a great idea, SSS lacks anything resemble a decent grasp of d20 mechanics. As a result the racial levels are uninspiring and rather bland. The handling of forsaken also leaves something to be desired (like, d12 HD perhaps?).
Chapter 3: Classes
Arcanist: while I love the idea of building paths of magic into the core arcane class, building the PrC benefits ALONG with Arcana is extremely overpowered. Taking the arcanist class is like taking levels in wizard AND getting all the benefits of a 10 level prestige class. *broken*
Healer: same as the arcanist.
Hunter: There is no need for this to be a 20 level core class, and worse the class abilities are rather lame. You can make 1 poison attack per 3 levels per day? Woo hoo. Aspects were a neat idea, but the execution is poor.
Paladin: God, things just keep getting worse. The replacement of smite evil with the holy strike mechanic was a bad choice. The execution of auras was even poorer. Auras are a *continuous* benefit. Look at the marshal if you want a good idea of how auras should work.
Rogues: Have been changed to grant 1 special ability starting at 3rd level and every 3 levels thereafter. Not sure if this a good thing or a bad thing.
Scout: Lame when it came out in the Warcraft RPG, still lame in the WoW RPG. Give me a non-spellcasting ranger any day.
Tinker: I refused to speak on wacky mechanic tinker-gnom...I mean goblins.
Chapter 4: Prestige Classes
Archmage of the Kirin Tor, Assassin, and Duelist: Ooh, you renamed the archmage PrC. Aren't you clever. NOT. If you are going to include PrCs, frickin' make them original or at least add new abilities. Reprinting material in the SRD is so very weak.
The remaining PrCs are fairly well balanced.
Chapter 5: Skills
No comments here.
Chapter 6: Feats
This is really what drove me insane with the Warcraft RPG and now with WoW. SSS/Fiery Dragon/whatever random mooks they had write this book has a piss-poor grasp of how d20 mechanics work, and how to balance benefits. The vast majority of new feats (not the reprinted SRD material) offer clunky mechanics and too much power for non-epic feats.
Biggest Offenders:
Bash: The mechanic is one of the worst I have seen. It should follow the same basic rules as Stunning First or simply function on a critical hit.
Battle Shout: What is the action required to issue a battle shout, and how long does the benefit last?
Block Spell: This is better than Epic Counterspell. A hint: if your non-epic feat has the power of an epic feat, then it should be an EPIC feat.
Bloodletter: Continual hp damage through bleeding on a critical hit. There was a reason it was changed to constitution damage in 3.5.
Brilliant Leadership: Granting bonus spells to your followers is the vaguest wording I have read. Especially since the followers gained through Leadership almost always CAN NOT CAST SPELLS.
Careful Strike: Grants a +4 bonus to Attack and Damage. Should be one OR the other, not both.
Challenging Shout: Fighters are not tanks from the MMORPG.
Counterattack: It a weakened version of Agile Riposte from d20 Modern.
Deflect Spell: Broken, and I don't want to get off on a rant here

Drums of Courage: Grants +2 attack and damage rolls and saves versus fear, and lasts for as long as you play and 5 rounds after. Has Perform 5 ranks as prerequisite and grants you the inspire courage ability of an 8th bard with no limit on uses: BROKEN.
Ok, enough on feats. By now the lack of understanding on how d20 feat mechanics work should be apparent by now.
Chapter Seven: Description
Lots and lots of fluff and flavor. This chapter, along with the introduction are the best parts of the book. Mainly because there are no mechanics for the designers to screw up.
Chapters Eight, Nine, Ten, and Eleven
These chapters deal with equipment (non-magical). No rant here. One note though: Chapter 11 deals with tinkers and technological devices. I have pretty much ignored this section through all the incarnations of Warcraft, so I will refrain from commenting on it here.
Chapters Twelve & Thirteen
Combat and status conditions. Nothing new here.
Chapter Fourteen: Magic
Ok, now for my RANT. All the Warcraft computer games have spellcasters spend mana to generate effects. WotC released spell points (aka MANA) as OGL rules in Unearthed Arcana well before this book was written. Rather than adopt them and actually make the d20 game resemble the video games they went with the traditional Vancian system. This makes my blood boil.
Chapter Fifteen: Spellcasting
Rules for spellcasting, ala the SRD.
Chapter Sixteen: Spell Lists
Because apparently including the class spell lists in Chapter 16: Spells didn't make logical sense.
Chapter Seventeen: Spells
Much like Chapter 6, this section is full of mechanically poor spells that are meant to represent the various spells found in the game. I would give you a full list of biggest offenders, but I'm feeling lazy so I will just list two here:
Blazing Column: A 4th level spell that inflicts 1d6 points of damage per 2 caster levels for *3* rounds, does not allow a saving throw against the damage, AND then does another 1d6 points of fire damage for 3 more rounds.
Brilliance Aura: Cast spells for free with a successful Spellcraft check. Are you insane? I do not care that the DC is 30 + twice the spell level. At 13th level with an Int of 18(24 w/headband +6) and an item that grants a +10 competence bonus on Spellcraft checks I can have a Spellcraft score of +29. And that is without even trying hard. Say I average a 10 on my check. That is a 4th level spell for free, for 1 round per caster level.
Chapters Eighteen, Nineteen, and Twenty
All miscellaneous topics. Chapter 18 does include the use of hero points. I loved the idea of hero points in Mutants and Masterminds, but I do not like how they were executed in WoW. Shocking news, right?
In a nutshell let me sum it up for you: If you are going to buy one Warcraft book, buy
Manual of Monsters. Beautifully produced, chock full of Warcraft beastie goodness, and except for the epic NPCs in the back, AND 95% mechanically sound.