I think Gamon would have been better if he had been Warmaster Blackhorn in Dragon Soul (and thus, his full name would be Gamon Blackhorn). It would have explained how he got so powerful in Cata (sold his soul to Deathwing), it would have made him a bit of a tragic figure (he turned to Deathwing because he was downtrodden and depressed and lonely that everyone always picked on him for no reason when all he wanted to do was to have a drink, and how nobody liked him), and would have ended his story. And it would have given a boss in DS some familiarity instead of "Oh yeah some random henchmen shows up".
On a similar note I would have given Hagara more of a backstory; probably something related to her being in love with Thrall and bitter/jealous over him choosing Aggra, so she turned to the Twilight's Hammer to get power over the elements to show Thrall that she would be a better life mate. There would be a tragic scene when she's defeated of her apologizing to Thrall for what she's done.