I just got Descent, and am planning to get expansions for it as well (mostly because I can't stand having a game that has expansions, and not owning all of them - it's just the way I am). So I understand getting RtL is mandatory for faster games and a longer campaign. I believe the spawn cards that WoD and AoD add are just shuffled into the overlord deck, and the new weapons and heroes are compatible, so there are monsters from those expansions in the dungeons, and their traps and all can be used there as well - right?
That leaves no place for lieutenants and bosses from those two expansions though (unlike ToI, where new cards for RtL were introduced with the expansion itself)
Am I missing something, is FFG planning to add compatibility support with a card mini expansion or something, or am I missing the point, having merely glimpsed into the rules, and there is no problem in the first place?