So, personally im looking forward to this ALOT. I've never been massively keen on playing RTS games online, im more looking forward to the extra campaign missions this will offer.
This expansion will be based around the Zerg portion of the story, as Wings of Liberty did with the Terrans. Only time will tell what they have planned for Protoss.
Blizzard seem to think this will be released this year, but we all know what they're really like with release dates.
Well, if you were a follower of Starcraft, that 45 seconds of video I posted gives you a pretty damn good idea of what's going to happen. Infact, 1 word can sum it all up:
Just gonna go off topic (Sorry Justicar): Blizzard have there own cinematic team, so they use it to create trailers detailing about the storyline so when the player goes to play it, they have a basic concept of what the game is about. Also a cinematic trailer boosts sales. That's why a lot of game company do it now. Because lots of people enjoy watching them and spread the word, "Have you watched this?"
On Topic: Never played starcraft but this trailer is good