As a sequel, Dragon Warrior 2 was a game that delivered. Nowhere is this more clear than the Overworld map. Allow me to... illustrate (pun intended.) Have a look at this:
In that little box there, is the original map from DW1. Yes, not only did Dragon Warrior 2 introduce Enemy Groupings, a party of three characters to play and a ship to cross the sea, but it also expanded the world map, so greatly that the entire map of the original game is able to fit in one corner of our new, expanded world. Each one of these additional continents is full of towns and dungeons for you to explore. You just can't beat that.
Enix could easily have invented a new world, of comparable size to the original. They could have introduced new features, or simple shuffled around the old ones. Instead they built a much larger world around the location of the original map, the inclusion of which is not only great for the sense of scale, but also a sense of time and history (Dragon Warrior 2 takes place 100 years after the first game).
P.S. There is some loss of detail between the two maps. The continent of Alefgard is actually slightly smaller than in the first game. Hills no longer slow you down as you walk. But these losses are small in comparison to the amount of real estate you gain.