Fun Fact: Dragon Quest III was so successful in Japan that developer Enix decided to not sell further Dragon Quest games in Japan until the weekends, so as not to disrupt public school schedules.
Dragon Warrior III was a top-down exploration, first person turn-based combat RPG and the final game in the original Dragon Warrior trilogy. It had a much larger and more open world to explore, and introduced a day/night cycle. Players had the ability to recruit and dismiss party members at will, and a new class system allowed supporting characters to learn multiple sets of abilities once they had leveled high enough in their base class.
While Dragon Warrior III was a huge success in Japan, it was released in North America after 16-bit consoles had hit the market. American audiences, who lacked the same cultural buy-in as Japanese audiences, had turned their attention to flashier, newer games. It was also a game meant for the hardcore JRPG fan. As is the case with this genre, the deeper and more complex the experience became, the more investment it required from the player. North American audiences did not seem willing to ante up and the game performed more poorly in that market.