The expansion will offer two new classes, a new region, and a continuation of the previous expansion's story. Blizzard has long been hinting that players will have to face Mephisto himself, so the stakes are high.
Blizzard traditionally makes strong story trailers, and the new CGI trailer is no exception. It conveys the atmosphere well and leads into the events of the expansion.
The trailer shown is essentially the beginning of the Lord of Hatred story. Those who plan to play the game without spoilers should postpone watching it, as the video reveals a key plot element of the expansion.