It seems a lot of people here need to learn the difference between a teaser and a trailer. They are very different things and serve completely different purposes. As a teaser, this was perfectly fine.
Also, Blizzard hasn't put out an actual trailer (the ones with story and voiceovers and such) for a patch since Patch 4.2. Unless you count the MoP cinematic, which I don't. Seems they now prefer to include those as in-game cinematics instead of putting them on youtube.