The original Dawn of War provided a great example of a very talented and diverse modding community. The first type were the graphics guys. Higher resolution textures, reworked GUIs, and expanded visual customization options were the most common additions. The second type were the faction guys. This was essentially just cloning existing assets and changing them to introduce new factions, but in some cases some original content was produced. The true difficulty of this type was the sheer amount of work that had to be done; everything from skinning new and cloned models appropriately, to balancing any new combat mechanics. The third type were the mechanics and AI guys. The latter was supremely represented by the Dawn of AI crew, who were so good and thorough that several of the largest factions and mechanics mods incorportated their work. As for mechanics, these rewrote every bit of stats and combat interactions from the ground up, whether to better represent tabletop rules, or to provide a more complex and interactive decision-making process when building your army.