Dragon Warrior was the first true RPG for the NES [Zelda was the first RPG]. Though fairly basic it become a  very poplular game, very quickly, especially in Japan where Dragon Warrior VII was released. This game introduced  level building, turn based battles, Hp and Mp all to Americans for the first time. The game series unfortunately started to decline in popularity in America and no DW games past the fourth one have been released in America. The original however was rereleased along with DW II for Game Boy color as well as to the NES.

Dragon Warrior Walkthrough
Dragon Warrior Review
Dragon Warrior Items
Dragon Warrior Levels And Spells Chart