Fun
There are a lot of possibilities to this game, and a lot of outcomes. How you design the dungeon directly affects your preparedness for the dragon, whether it's the experience of your characters and how many are 15, or just their equipment. In my case, which is probably a bit of a rarer one I assume, a ring that gave me instant resurrection dropped (Full health at 0% HP rather than at 30% like some of the others), so my rogue single-handedly slayed the dragon simply because he was impossible to kill, but not before my highest level cleric got killed.
Worth playing through more than once in my opinion.