The editor allows you to create your own custom, complete campaign with levels, dialogs, quests, etc. It's (mostly) the same tool they used to create the DOS2 campaign but it does have some limitations. For instance, we are not able to add new sounds to the game so your wish to have custom voice overs is not feasible. It is essentially a professional development tool, so it is considered complex by many who pick it up, as you alluded to.