I'm not a huge consumer of Warcraft merchandise, but a few years ago I stumbled upon a copy of The Warcraft Archive in a bookstore and decided to buy it on a whim. It contained four short novels, ranging in quality from pretty good (The Last Guardian) over reasonably entertaining (Lord of the Clans) to occasionally cringe-worthy (Of Blood and Honor) and humorously bad (Day of the Dragon). Since most of what I heard about other WoW novels seemed to firmly place them in the latter two categories, I shied away from buying any more... until I spotted Rise of the Horde in another bookstore the other day and decided that since I had liked Lord of the Clans well enough and this was by the same author and also about orcs, the chances of me enjoying it were pretty good.
I'm happy to say that my assessment was spot on. Rise of the Horde is no literary masterpiece, but if you're sufficiently interested in the plot and characters it will keep you entertained, maybe even hooked. I was actually a bit disappointed that it ended when it did, not because it didn't make sense, but because I know that other interesting stuff happened after the last events in the book and I would have liked to just read on.
I'm not sure how interesting the book would be to anyone who already knows the story of the Rise of the Horde in detail, but I didn't, so it was. As someone who didn't play any of the previous Warcraft games I really appreciated the opportunity to read about some of the related events in novel form. Of course there's always WoWWiki if you have lore questions, but to me reading WoWWiki is like reading a history textbook - okay for quick fact checking, but I'll be unlikely to retain anything but some scattered bits and pieces for longer than five minutes. (Or maybe it's just me who's like that with history textbooks...) I do much better when I can look at events as a story, with context and human (or orcish as it may be) relations laid out in a logical manner. Finally I won't have to be confused anymore when someone mentions Ner'zhul or Gul'dan!
Also, it may be a bit silly but I really enjoy reading about the same fantasy world that I play in every day. Good old Velen, I know he's just as ugly in the Exodar as the book says he is! Ata'mal crystal? Oh yeah, I remember taking that off some demon dude in Netherstorm. And so on and so forth... though there's sometimes also the negative side effect of the images of the game world conflicting with what I'm reading. Like me thinking that there's no Draenei city other than Shattrah in Terokkar, I've explored it all so I know! Or frowning at the description of K'ure being buried under a lake when he's just floating around in the back of Oshu'gun in the game.
Still, overall I can recommend the book as good, light entertainment for anyone who wants to know more about that particular bit of the lore and enjoys reading about the same virtual world they play in every day.