The opening scene informs the player that it has been three years since the events of Ys I and Ys II. Adol Christin and his friend Dogi are on a journey to Dogi's hometown of Redmont. Upon arriving, they learn that the townspeople are being threatened by men from nearby Valestine Castle. Always ready for adventure, Adol decides to assume the task of helping them out.
The gameplay of Ys III is a sharp departure from the previous two games. Instead of the previously used top-down camera view, Ys III has become a side-scrolling platform-action styled game. The combat has also changed: the player must push a button to make Adol swing his sword and attack enemies.
The RPG-style statistics and experience system still exists in Ys III, however. A new addition to this area is the "ring" system: Adol can acquire and equip rings that provide special effects while equipped. A new attribute, "Ring Power", is consumed while rings are active.
Source: Wikipedia, Ys III: Wanderers from Ys , available under the CC-BY-SA License.