Three additional concepts maybe worth stressing:
Flexibility: A higly customizable engine that allows different rulesets and mechanisms for all kinds of scenarios, like e.g. sci-fi, fantasy or steampunk. This includes freely definable races, classes, spells/powers, traits, skills, effects, items, creatures, areas... and also encompases mighty scripts in c# that can be freely changed and adjusted by indidividual authors.
Ease of use: A toolset that enables non-coders to tell their stories with minimal barriers to entry and in an efficient way, allowing authors to bring their projects to live in their spare time, despite following a normal work and familiy life.
Growing campaigns: A savegame system that allows authors to gradually enlarge their game worlds without forcing players to restart from 0 with eahc new patch/new content coming in. In other words: old savegames will always be usable even after the campaign has grown by a few areas, quests, characters, new rule options, etc.