Once players have played all the "out-of-the-box" scenarios several times, is it easy to make their own? Is there some simple point-based system in place to ensure scenario balance?
From FFG's Quest Database webpage -
Are there any guidelines for creating a new quest?
In terms of content: Keep it clean! Descent: Journeys in the Dark is a game of adventure and heroism against foul monsters and an evil overlord. There's no call for foul language and other inappropriate content. In terms of gameplay: Let your imagination go wild! There are no hard and fast rules as to what makes a quest fun or balanced, only imagination and common sense are your guides here. If you like, here are some things to keep in mind.
* As the heroes gain new treasures and abilities, the Overlord should gain more powerful monsters.
* One glyph per area is a rule of thumb - too many glyphs and the Overlord will never be able to take all the Conquest Tokens away from the heroes. Too few and every death becomes a crippling setback.
* Tricks, riddles, and puzzles are fun, but only if the Heroes have some clues to work with!