Dragon Quest II
Dragon Quest II may be viewed as one of the more awkward stages for the series, but as an iOS RPG it's an excellent option. It's a massive change in the familiar formula already established in the last game, and while it's finding its footing was a little difficult for the game when it first released, it's the perfect mobile adventure otherwise, with a few snags due to its age.
Dragon Quest enters the next level of JRPG status with the addition of more characters to the group and groups of enemies as well. Additional attacks, status effects, and other significant changes to the battle system make for an overhauled journey that allows for additional strategy and planning.
You can go basically anywhere you'd like to on the map as well, and this degree of freedom makes it feel much more suited to the mobile platform since you're not restricted to only the areas you're "ready" for.
Additionally, this version incorporates a gorgeous symphonic soundtrack and simple portrait-styled layout makes it simple for playing with one-touch gestures.
This could very well be one of the most difficult Dragon Quest titles in the series, with some particularly memorable dungeons that feel artificially difficult simply for the sake of being so. While some alterations have been made to ensure the game is a little more difficult than its original iteration, it can still be quite frustrating, especially if you're used to the sliding difficulty scale in the previous Dragon Quest games.
Dragon Quest II is a game from a simpler time that translates well to the mobile platform, with plenty to offer new and old players. It can be much more frustrating and unforgiving than the other titles in the series, but in the end it's very much worth your time.