I have a few ideas here:
For the moment, the game is very short, going down to floor 7 and up again. A few ideas to extend, and shorten it.
Floor size option: Changes the size of the floor (Small, Medium, Large)
Difficulty options (Easy, less monsters, weaker lich) Medium (Normal monsters, Lich) Hard (More monsters, tougher Lich) Expert (Worse loot, Smarter mobs, follow you between floors, even more monsters)
Option to edit where each theme occurs, and how many floors of that theme, even turning off certain themes, final floor cannot be changed.
Example: Cave disabled, four floors of normal dungeon, 2 floors of sewer, bottom with Lich
Example 2: 5 floors of dungeon, 10 floors of caves, bottom with Lich.
Along with difficulties above, monsters would change slightly, like on hard and expert, new aspects, such as following you between floors.
Instead of monsters respawning when you get the orb:
Timer appears and gives you 5-15 minutes to escape the dungeon, depending on the number of floors and difficulty.
Optional "Puzzle rooms", along with the addition of jumping, for things such as jumping puzzles, mazes, etc.