I dislike the fact that Blizzard made the Death Knight so damn powerful. I mean, really, mine can finish quests at my level that are meant for groups of 3 people.
Sure, it's a hero class, and sure, you have to have a level 55 character, but Jesus! Most, if not every account has a level 55 in the list.
This results in having about 30 Death Knights in a zone, and about 1 or 2 original classes.
I'm not complaining because I don't like them. I love them! It's just that Battlegrounds aren't going to be very fun anymore, seeing as how more than 50% of the players will be overwhelmingly powerful Death Knights.