They just have bigger or smaller hitboxes, models, and slightly different abilities. Dreg = Thrall = Goblin = Psion Vandal = Acolyte = Hobgoblin = Legionary Captain = Knight = Minotaur = Centurion Servitor = Wizard = Hydra = Collosus Even the ships can all slowly bombard you Fallen Skiff = Hive Tomb Ship = Cabal Harvester (Vex have a dark cloud) My point is the ideas from one race to the next don't vary all that much and are kind of lazy. It's even worse that every enemy is recycled every expansion without fail.