First of all, there a huge difference between LORE and RP some people is missing.
Im a lore fan. i really like reading about the world im playing in, and i have to say that WoW's lore is pretty damn good.
Im not an RPer, however. When im doing instances, my main concern is about figuring out mechanics and discovering faster or more effective ways to kill bosses, not trying to play a role in an imaginary story.
That being said, i believe the new dungeons goes a lot past the point of offering us the lore behind them, with extensive comic-like dialogues where the characters explain the story.
Im thinking about the Arcurion/Archbishop encounters (what the heck, when did he turn evil? he first help us get inside and suddenly hes bad. and whats worse, Thrall seem to knew about it!!), and to a less extent to the different parts in the End Time instance (they are short enough and kind of justified by the fact were being led by Nozdormu. They also dont stop the party from starting the pulls).
It just becomes a pain instead of an enriching experience about lore, specially when its the 5th time running throught it. This method i believe works exactly against its purpose, killing whatever "epic feeling" a given instance should have, for an history lesson.
I dont mind long speeches from time to time. actually, it comes to my mind Scourgelord Tyrannus on PoS and his awesome taunt before the fight
Alas, brave, brave adventurers, your meddling has reached its end. Do you hear the clatter of bone and steel coming up the tunnel behind you? That is the sound of your impending demise.
I understand there a very thin line between enriching an instance with the lore behind it, and just plain flood the gameplay with history lessons, or doing senseless instances where players dont understand whats going on.
I would propose a more extensive usage of the Dungeon Journal (GREAT tool so far imo). It already has a short summary about every boss´ lore (or at least some info) before the mechanics explanations so i think it would be a nice way to go, offering the lore to whoever wants to get more informed about it, like me, and leaving the gameplay smooth and uninterrupted. Keyword here is the OPTION to access the lore.