There's something about shamans that gets us thinking and talking. Whether it's something as simple as the proper pronunciation of "shamanism," or something as profound as a shaman's humility in relation to the source of his or her power, the lore and ideology of the shaman class often resonates with players more than many others in the World of Warcraft.
One reason for this is that shamans have been such a pivotal force in the lore, possibly more than any other class in the game (depending on your point of view). Other classes, such as warriors, or paladins, come as a sort of pre-defined archetype in fantasy games that don't seem all that different from their original forms in other fantasy settings. The actual beliefs of a priest, for instance, don't seem to matter so much to many players, so long as the class can heal like we expect them to. Even the druids, with their central place in night elf society, sometimes seem more like nature-based magic users rather than true philosophers in their own right.
Shamans, however, have a major burden to bear in one of the central plot shifts of the Warcraft storyline -- namely that the orcs, who entered the Warcraft stage in the Warcraft 1: Orcs and Humans computer game as rampaging demonic evildoers bent on destruction, and actually turned out to be a peaceful race that just got tricked into being evil. Shamanism had to be much much more than just an archetype with some special powers -- it had to be a way of thinking, a system of belief that could be taken over by demonic corruption and yet at the same time act as a beacon of truth and goodness once that the demonic taint had been defeated. Shamanism has got to be complex and profound, or else the story wouldn't make sense.