The trial includes the following, I am not sure if you need to purchase MoP xpac if you decide to carry on.
While you're back in Azeroth, you'll be able to check out the latest improvements to World of Warcraft, including:
New Playable Race -- Pandaren: Decide whether to side with the Alliance or the Horde as World of Warcraft's first neutral playable race, and explore their unique starting zone: the Wandering Isle.
New Playable Class -- Monk: Unlock the secrets of pandaren martial arts and do battle as a damage dealer, healer, or tank.
New Continent: Explore the lush Jade Forest, treacherous Kun-Lai Summit, and other exotic new zones of Pandaria designed for high-level characters.
Pet Battles: Challenge other players' companion pets with your own collection in a new tactical mini-game. Level up your companions and discover pets in the wild to round out your roster.