I would probably design and populate a core of the dungeon for the adventure at the start, while placing a few upside down possible destination tiles at the edge. While the core adventures have some nice details to them, I think that many could use some different core structuring to the game. The game play is more strategic where you are resource managing your hit points than tactical where you are trying to optimize you positions to make best use of you abilities. While this might simulate exploring a total unknown dungeon by torch light, you find your hero essentially surprised every turn.
It is not that these issues make the game hard, it is just that you lose by just getting hit by a bad series of traps or monsters even if you defeat them at the first time you can act. You can not explore a new tile, but this automatically causes a new encounter card which means generally more damage. So I would say regardless of who you are or what you do every new tile you open averages probably 1.5 damage units to you before you can do anything to really influence the results. The new monster essentially gets to attack you (or another hero) right away. This ends you turn and immediately places a new tile there with a monster and possible encounter card(these are usually just one off attacks). You expose a new tile by stopping your move at an open edge of a tile and exploring the new tile. So a lot of the focus of the game is getting through that tile stack while taking the least damage possible.
Often the adventures involve getting to a specific tile so the rules have you place this tile either at a specific depth in the stack or in a range by shuffling it with a small group of tiles and then inserting those at a specific point. Now to review the way the game plays, each adventure starts with you organizing the tile deck.