I would like to have a sense of progression to more difficult, unexplored environments the farther you get.
Considering that the game is called Delver's Drop, it seems natural for the progression to be downwards. For example, in Spelunky, the progression is: Caves -> Underground Jungle -> Ice Caves -> City of Gold (though you have to meet certain conditions. Otherwise, you go straight to the temple) -> A Forgotten Temple -> Hell (Must go to the City of Gold first). There is very clear, and sensible, advancement to more and more dangerous environments as you venture farther into the game.
Upon saying this, however, there is a sense of mystery behind the dungeon of Delver's Drop. Despite the fact the you are going down to the mountain core, the progression may be different than what you might expect.