Critics have often commented that Willow borrows many elements from George Lucas' earlier success, Star Wars.  Let's take a look at some of the similarities:

Star Wars Willow Description
Luke Skywalker Willow Ufgood The Main Character; a farmer in a remote area who is swept up in a quest to bring about the downfall of a Tyrannical Ruler.
The Force Magic Mystical Power that the main character learns to master during his quest.
The Emporer/Darth Vader Queen Bavmorda The Tyrannical Ruler, master of the Mystical Power; plans to enslave the universe.
Alderaan Tir Asleen The Main Character's Initial Destination; a peace-loving kingdom where he will supposedly be safe.  When he gets there, he finds out it has been destroyed by the Tyrannical Ruler.
Obi-Wan Kenobi The High Aldwin The Main Character's older peer who has experience with the Mystical Power; he lets the Main Character know that he too has potential to master the Mystical Power and sends him on his quest.
Han Solo Madmartigan The Rogue-Hero; he starts out as a criminal who reluctantly follows the Main Character on his quest and ends up believing in the cause.
Lando Calrissian Airk Thaughbaer The Rogue-Hero's old friend; starts out actually betraying the Rogue-Hero, but eventually redeems himself by joining the quest.
Princess Leia Princess Sorsha The Princess; daughter of the Tyrannical Ruler, whom she ends up fighting against.  She falls in love with the Rogue-Hero.
Yoda Fin Raziel The Main Character's Mentor; trains the hero in the mystical power; has a humble appearance that teaches "you can't judge a book by its cover."
C3P0 and R2D2 Franjean and Rool Bumbling sidekicks of the Main Character; their chemistry provides much comic relief. Lucas admired the way Kurosowa used two bumbling peasants for comic relief in the Hidden Fortress and borrowed this concept for both Star Wars and Willow.

Other parallels can be drawn as well: