I saw some debate over priest mechanics so i want to add something on it. I am not entirely sure if these were mentioned partially or totally and neither sure all are true but here we go:
Priests were special in their own way depending on their races. For example, like someone mentioned above, dwarven priests had the fear ward ability and no other priests had that. Night elf priests had some kind of starfall skill as i remember but it was a single target ability, not like todays laser chicken's aoe stuff. Undead priests had devouring plague special to them and that made them particularly OP in many pvp situations (combined with will of forsaken) and also probably the only serious shadow candidate. I dont remember what human or troll priests had. If anyone else remember the race specific priest spells please feel free to add.
And i also strongly believe that these race specific specialities made it much more fun. Sadly blizzard homogenized priest like they did to everything in the game