@Shev: You find Knaak drags on? You'd hate any book by Dan Abnett... I don't find Knaak drags on and have read through all the books up to Arthas without issue. On the other hand I didn't even get half way through the first Horus Heresy novel because Abnett managed to spend what felt like a quarter of the book describing a man walking down a street (Nothing happened, it was an empty street), eventually finding a bar and then getting drunk.
Personally, I'd say it depends on what part of Warcraft's lore you enjoy. I really loved the whole War of the Ancients trilogy but was a bit blah about Rise of the Horde and Tides of Darkness. Whereas people I know who are Horde fans felt the other way around with those.
It's a shame neither of the archives are available on Kindle otherwise I'd suggest getting the first archive as that has a story from each of the four main writters and will give you a better idea of what books you are likely to enjoy after that.