I'm a hobbyist Voice Actor and so I spend a lot of time listening to voices and reading dialogue lines. Over the seven years of my playing WoW I've taken notice of pretty much every voice I've ever heard in game. That's led me to some amazing voice actors, but it's also made me grow incredibly tired of the writing of WoW's characters, and made me very conscious of the bad side of it all. My argument is, while I know that there are so many bosses that need lines, they are so devoid of creativity that Blizzard really need to start upping their game. There can be so much done to each boss, but they are given stock lines. Even in MoP we are introduced to so many 'I will consume you!' lines. I know that it's not important to most of you, but it is important to some, and it's key to giving bosses soul.
I've got a video here that I spent A LOT of time making. It should showcase how absurdly repetitious things were, and still are. There's a few interesting things in there that I managed to find.