I know it seems traditional to hate the returned king of Stormwind, because he's getting all aggressive with the Horde and because he's hatin' on everyone's favourite orc, Thrall, but I think he's great.
Why? Well, for one, I think his complete and utter mistrust of the Horde is completely justified, as Lorecrafted points out, in great detail. And that's without mentioning the fact he was enslaved and forced to fight by orcs, or him witnessing the Warsong Clan's atrocities in Ashenvale, or that he's just seen off one of the Black Dragonflight, who have allied with the Horde in the past...
Varian is very much Thrall's darker opposite. The War Chief has been repeatedly exposed to the best of human nature down the years, while the King has had the very worse of Orc behaviour thrust into his life. And his charge that Thrall doesn't have a good grip on the Horde is more than justified. We might not be comfortable with his actions, or his view, but they are understandable, and just possibly right.
And my goodness, we didn't have this level of plot advancement in WoW a year ago, did we? Blizz really have driven the narrative aspect of WoW forward with this expansion.