The guy is epic and should be immortalized solely for that voice-over.
I really hope for a live action movie that (obviously) makes heavy use of special effects.
I really think the story will be centered around a human character, regardless what it may be about. Simply for cost effectiveness and ease of production. If not Arthas; Rhonin's side of The War of the Ancients would be an awesome story to see on screen. But I'm a little biased there since I just read that book.
CGI characters who are played by real actors in front of a green screen, think Golem from LotR, would probably be utilized for races that would be almost impossible to create costumes for.
Seriously, I've been following this rumor for 5+ years...I've thought about it from almost every angle. Blizzard cinematic-style CGI would be awesome, but I don't think it would appeal to a wide enough audience...especially with the PG-13/R rating the film would more than likely receive. I think the only way to seriously make money with this is to make a live-action LotR/Hobbit style film.