Of the two Mario RPG sub-series, Mario & Luigi is much closer in tone and spirit to Super Mario RPG on the Super Nintendo. That's because M&L developer AlphaDream consists of former Square employees who worked on the plumber's first role-playing adventure.
To commemorate the release of Mario & Luigi: Dream Team, IGN interviewed key Nintendo and AlphaDream members on the series' development history. Yoshihiko Maekawa, Super Mario RPG co-director and Dream Team co-producer, explained how Nintendo gave AlphaDream permission to inject Luigi with an original personality for the first M&L. He also addressed fans' desire to see Mallow and Geno return in a future M&L installment -- Geno made a super brief cameo in Superstar Saga, if you recall.
The big element that Super Mario RPG was known for and saw further evolution in the M&L series was the innovative timing-based battle system. "That was very much inspired by a children's toy that was available in Japan at the time," Maekawa recalled. "It was like a large laptop with these buttons that would play music. You had to press the buttons with good timing to the music. It was that idea, having gameplay built around timing button presses, that inspired me to hybridize these two genres of game, to get a little bit of action and RPG into the same game."
Be sure to read the full interview at the link below.