Mop has loads of new characters, but also development for a lot of old ones. Jaina and Lor'themar both got some big developments, along with Varian, Anduin, Rommath, Aethas, Taylor, Nazgrim, Tyrande, Baine, and obviously Garrosh, Vol'jin, Thrall.... and loads of others.
i love what they've done with the Blood Elf leaders and Varian/Anduin myself.