It suits the sort of player who likes checking in rather than camping beside a game. Send the party underground, come back later, spend the accumulated resources, and decide who deserves the next upgrade. As the guild and town grow, even routine dungeon runs start to serve a larger purpose.
The unlocked full version opens up the complete progression loop, from hero upgrades and party combinations to offline gains. First-person dungeon crawling gives the battles a closer feel, while the idle side lets the game keep moving when you are elsewhere. A decent little time-killer for RPG fans who enjoy watching a squad slowly come into its own.