Road to Legend is an amazing addition to the Descent series. I've been running two RtL campaigns in which I have clearly crushed the Heroes. Everybody is enjoying the game a lot but, after so clear OL victories, many players were complaining about the balance of the campaign.
One thing I have realized after my two first campaigns is that in RtL, as in other complex games, the balance is also a question of experience (if not more than the game design) and, whereas the OL has a relatively easier time to come back if he makes early mistakes, the Heroes don't have such advantage in RtL. That means that early mistakes in the campaign will probably spell doom for the Heroes later on... But this is a problem of the Heroes' experience, not of the game design... With this in mind, I remembered the difficulty levels of the game Doom and thought they could be used also in RtL... So this is mainly for those of you that are considering starting a campaign.
Of course, the main idea behind this post is using difficulty levels. I propose here some, but you could tweak them to your taste.
Beginner Level ; "I'm Too Young to Die" (for the first RtL campaign): At the beginning of the campaign, the Overlord does not get 15XP to spend. Also, Sir Alric Farrow does not start on the board (he still costs 0XP to the OL, so it will be easy to recruit).
Intermediate Level ; "Let Them Come" (after the first RtL campaign; so long the Heroes have not won): The OL initially gets 15XP to spend but he cannot spend these points in Treachery or Lieutenants. Sir Alric Farrow does not start on the board (his cost is still 0XPs).
Advanced Level ; "Hurt Me Plenty" (after the Heroes win their first campaign): Play as with the original rules with the following extra: Leaders in encounters and Dungeon Levels get their bonuses multiplied by 2 in Silver Level and multiplied by 3 in Gold Level.
You could also create extra insane difficulty levels if the Heroes are having it too easy. I would suggest playing Copper Level as published because it is already hard enough even for experienced players. It is only in Silver and Gold levels that the game could be too easy for the Heroes.