Shamans are probably one of the most diverse classes in the game, as they are a mage/healer/warrior class that can take on so much and heal themselves at the same time. And, depending on how a gamer specializes their shaman, they can enhance special areas that they want to use in the game, such as healing.
One of the main things that shamans are known for are their totems, which help them with mana regeneration, defense, strength, and more. These can be invaluable in groups and instances, as party members benefit from these as well. The shaman was at first only a Horde class, and the Alliance had the paladin, but now the Draenei can become shamans, which give those Alliance players a great way to check out this awesome class.
Shamans can use a wide variety of weapons and armor, which also give them a great way to enhance your play if you choose this awesome class. Plus, when it comes to group play, you are never at a shortage of finding one, as groups will fight over your services since you can be a DPS, use your totems, and be a back up healer and resurrect fallen members when needed.