Here are some clips that give a glimpse of what you can expect WOTLK will be like once it is released. The footage was taken from various sources such as worldofwarcraftmovies.com

WotLK Landscape
WotLK: Azjol-Nerub Preview

This is a movie made to show the instance Azjol-Nerub. It is the kingdom of the Nerubians, and the leader, Anub'arak, is an ally of the Lich King. The movie features a small cinematic intro followed by the bossfights, shown through the perspective of a rogue.

Source: devlin.warcraftmovies.com

WotLK: Utgarde Keep Preview

Utgarde Keep is an instance in the Howling Fjords. It is filled with Vrykuls and undead beings, and it is a very dark and damp place. The movie consists of a small cinematic intro followed by the bossfights, shown through the perspective of a rogue. Utgarde Keep only houses three bossfights, which make it a short instance.

Source: devlin.warcraftmovies.com