Final Fantasy games for GameBoy:

Final Fantasy Adventure (Seiken Densetsu)
A Zelda-like Adventure Game that spawned the Secret of Mana (Seiken Densetsu) series. It introduced the Mana Tree, Jema Knights, and Moogles.
Final Fantasy Legend (Makai Toushi SaGa)
A Dragon Warrior-style RPG that spawned the SaGa/Romancing SaGa/SaGa Frontier series. It features exploration of many worlds on different floors of a central tower, in an ultimate quest to find Paradise on the top floor and be granted a wish by Creator. The character classes are Humans, specializing in weapon and armor use, Mutants, specializing in magic use, and Beasts, who can eat monster meat to gain abilities.
Final Fantasy Legend II
An unrelated game that also features exploration of many different worlds connected by a tower. This time the tower connects all the individual worlds to a single cosmic plane. Also, the player is on a quest to find his father. Character classes are Humans, Mutants, Beasts, and Robots.
Final Fantasy Legend III
In the rich tradition of Final Fantasy games, this one is set in a different universe from the ones before it, but has a vaguely similar storyline. The player travels through different time periods and dimensions to fight evil. Again, the player is on a quest to find his father. Characters can eat meat to transform into a Beast, and more meat to transform into a Monster, or they can install parts to turn into a Cyborg, and more parts to turn into a Robot.