An idea.

iPhone and iPad games, in my mind, should not be too story heavy or demanding on a player's time. While the App Store does have bigger, more involving games like RPGs, the top selling and most well known games are those repeatedly described as 'simple' and 'easy to pick up'. Mobile gaming is all about convenience; games that are easy to jump in and out of are more successful because they can be played during lunches or ten minute downtimes throughout the day. A list of the most popular iPhone games can be found here.

The top ten games are visually distinctive and easy to play. While they, like most games, take practice to become very good at, the average player can pick the game up and become familiar with the controls within just a few short minutes. Thus, the controls are 'intuitive'; easy to use and understand.

Replayability in hack-and-slash games is very important, especially when they're competing against the appeal of score-grinding in a puzzle game like Angry Birds. The randomization of dungeon floor generation is a way to combat this.

An extreme example of floor randomization can be seen in the RPG Persona 3. Players are required to navigate their way through Tartarus, a tower that only appears at midnight and leads toward an unknown evil. There are 265 floors a player must fight through in Tartarus, broken up by bosses every ten or fifteen floors. The process is kept from becoming too repetative by changing the layout of each floor every time it is traversed, and by having enemies increase slowly in difficulty.

While the combat in Persona 3 is the usual turn-based mechanic you would expect from a JRPG, it manages to achieve the objective of having a player repeat the same action multiple times without it becoming repetative. Floor climbing is broken up by visits to non-combat zones and social interaction. While the latter is not suitable for the game I have in mind, this gave me the idea of using a hub as a base of operations for the player; a place for them to view their achievements (enemies defeated, longest run made) and organize the items they have acquired while taking a break from the fighting sections of the game.