Cata is the first time WoW has progressed further in the story then Warcraft itself which only stopped at The Frozen Throne. So from Vanilla till WotLK we know the story before hand but in Cata, no one knows what is going to happen, so thats epic in its own way.

Whats more is Deathwing is a corrupted Dragon Aspect which equals or is even greater then the old gods. When the Titans created Azeroth they left 5 dragons to govern it after they left.

Nozdormu, the Timeless One
The massive bronze dragon chosen by Aman'Thul to guard time itself and police the ever-spinning pathways of fate and destiny.

Alexstrasza, the Life-Binder
The red leviathan chosen by Eonar to safeguard all living creatures on the world.

Ysera, the Dreamer
The lithe green dragon, and Alexstrasza's younger sister, chosen by Eonar to watch over the growing wilds of the world from her verdant realm, the Emerald Dream.

Malygos, the Spell-Weaver
The blue dragon chosen by Norgannon as the guardian of magic and hidden arcanum.

Neltharion, the Earth-Warder
The mighty black wyrm chosen by Khaz'goroth and given dominion over the earth and the deep places of the world. He was driven mad by the whisperings of the Old Gods and managed to drive the blue dragonflight to near extinction. He is now known as Deathwing.

I liked it when Illidan said "You are not prepared" though. WotLK's cinematic wasn't appealing to me as well.