I played a lot of WC3 story mode. I had found Starcraft such a revelation that it was impossible for me to not want to submerge myself in the combination of epic narrative and fun art and gameplay when WC3 came out. I had been largely a console gamer before this, so WC3's story mode was one of my formative PC gaming experiences, and also one of my first forays into hardcore fantasy fiction (aside from my dad reading the Hobbit to me before bed as a child).
So to finally see the end of that story play out, and experience in a more personal way so many nostalgic and sentimentally symbolic touchpoints, is very exciting to me.
Yes, many aspects of the story are cliched or predictable. Arthas is a reverse King Arthur, and the Lich King might as well be named Darth Sauron, complete with black outfit, flowing cloak, and spiky spires with magic eyes at the top. At least Arthas's motivation for his fall makes some semblance of sense, unlike Anakin's hubris and puppy love (if you even consider "Episode 3" to be canon).
I'm more interested in the epic feel around the whole thing, and the reactions of the world and the other characters to him. I'm expecting to see something awesome, and that's what's got me excited.
Jaina and Sylvanas will be able to finally resolve their long-standing Arthas issues. We'll see where the Ashbringer's story goes, what happens to the Mograines and the Saurfangs, and the fate of Bolvar Fordragon.
And Shadowmourne, which a small part of me is just too afraid to hope might be available, at least in some partial, gimped way, to 10-man raid groups. That story is something I'd really like to be able to take part in, rather than be completely shut out of solely because of raid size. I've made my piece with the other 10 v 25 crap (mostly), but man would I be excited to have a shot at that thing.