Dragon Quest. In its native Japan, this RPG series is regarded as one of the greatest RPG series of all time (It's even more popular than the Final Fantasy series over there), and the first game in the series gave birth to the modern JRPG.
In the United States, the series is not very well-known, the Final Fantasy series being the go-to RPG series here. Which makes Dragon Quest IX an underrated game, the first in the series to be released for handheld consoles.
Your character is a Celestrian, essentially an angel. You have justundertaken the task of protecting the village of Angel Falls, so you can earn benevolence for the World Tree. Enough benevolence causes the Tree to sprout Fyggs, which are needed for the Celestrians to move to another realm. However, a mysterious force attacks the Celestrians' home, separating them, and knocking your character to the mortal world.
You must now go on quests to collest the fyggs, and undo the twisted wishes of people who have eaten them. Over time, you can form a party, collect gold which can be used to buy new weapons and armor for yourself and your party, and eventually become strong enough to fight the force that attacked the Celestrians' home.
There are two features in this game I love. One is alchemy. By collecting various components from treasure chests and battling monsters, one can create various items, weapons, and armor. Recipes are hidden everywhere, and you can experiment with recipes of your own.
The other feature is that you see the monsters on the overworld. Instead of being caught in random battles, you can see monsters around you and your party and avoid them if you do not wish to battle at the moment. It's a great idea, and more RPGs should use this concept.
The only complaint I really had so far was that the game requires a LOT of grinding, especialyl if you are trying to get enough gold to buy better equipment and weapons for your party. It can wear on the patience at times.
If you're looking for an RPG to play for your DS, pick this one up.