1. They are sophisticated, refined and aristocratic
Having its origin in the patricians of Europa, the III Legion has always placed an emphasis on aesthetics and nobility. While remembrancers were generally disliked by the Primarchs and the Astartes during the Great Crusade, the Emperor's Children alone recognized that the development of artistry was as important to the life of a warrior as was training in the arts of war.
Fulgrim is one of the most fascinating and colorful Primarchs in the Horus Heresy. He was one of the first to flock to Horus' side and one of the first to grasp the infinite possibilities offered by Chaos to humanity, ascending to immortal Daemon Prince status in Amon ny-shak Kaelis. Brother Primarchs Ferrus Manus and Roboute Guilliman were slain by his hand.
3. Their style of war is elegant and decisive
The III Legion's style of war is unique. They are decisive on the charge, striking quickly, breaking their foes and slicing them down as they run.
4. They have a compelling story to tell
The story of the Emperor's Children is a tragic one. The transformation of the Legion is one from nobility and perfection to a lurid host consumed by experiential passion. From the start of the Heresy the Emperor's Children play a central role, including such iconic moments such as Murder, Isstvan III, Isstvan V, and the Siege of Terra.
5. They provide color and pageantry to a gaming table
The Horus Heresy armies are largely a somewhat drab lot. Most armies are colored muted shades of black, grey or white. The Emperor's Children have no such restrictions, and provide their players with unparalleled opportunities for creativity.