These were simply the coolest games made for the Intellivision.  AD&D was an action/adventure where you hunted down dragons and demons in their lairs, ultimately leading up to Cloudy Mountain.  Treasures of Tarmin, on the other hand, was a first-person RPG somewhat similar to games like Dungeon Master and Eye of the Beholder that would come much much later.  I can't even count how many hours of my life ticked away in front of these games...