I keep imagining this game to be similar to the free MMO Dungeon Fighter.
In that game you have sort of a city/hub where you can buy standard gear and learn new abilities/skill trees of your class. From there you choose from a bunch of different thematic areas that have a level range of how difficult it is and the recommended level of what the player should be. Every area has many levels with the last one having a major boss at the end. You can replay areas/levels as much as you want and can set to higher difficulties for better loot and such as well.
The Dungeon Fighter comparison might not be that far off. At least not where it concerns the level structure. They did say the game would be quest based. So there probably is a hub area where you take quests and then venture into the dungeon to complete them. Although it sounds like quests might allow players to take different routes to get to their end goal and many may have multiple ways of beating them.