TOP 20: Gamecube Games

Number 20: Lord of the Rings: Return of the King
First Released: November 5, 2003 (NA)
Developer: EA Redwood Shores

Number 19: Viewtiful Joe
First Released: June 26, 2003 (JP)
Developer: Capcom Production Studio 4

 
Number 18: Star Fox: Assault
First Released: February 14, 2005 (NA)
Developer: Namco

  
Number 17: Custom Robo
First Released: March 4, 2004 (JP)
Developer: Noise / Nintendo

Number 16: Sonic Adventure 2: Battle
First Released: December 10, 2001 (JP)
Developer: Sonic Team USA

   
Number 15: F-Zero GX
First Released: July 25, 2003 (JP)
Developer: Amusement Vision

Number 14: Star Fox Adventures
First Released: September 23, 2002 (NA)
Developer: Rare

Number 13: Luigi's Mansion
First Released: September 14, 2001 (JP)
Developer: Nintendo EAD

Number 12: Metroid Prime 2: Echoes
First Released: November 15, 2004 (NA)
Developer: Retro

Number 11: Pikmin
First Released: October 26, 2001 (JP)
Developer: Nintendo EAD

Number 10: Super Mario Strikers
First Released: November 18, 2005 (EU)
Developer: Next Level Games

Number 9: Mario Kart: Double Dash!!
First Released: November 7, 2003 (JP)
Developer: Nintendo EAD

Number 8: Animal Crossing
First Released: December 4, 2001 (JP)
Developer: Nintendo EAD

Number 7: Pikmin 2
First Released: April 29, 2004 (JP)
Developer: Nintendo EAD

Number 6: Super Smash Bros. Melee
First Released: November 21, 2001 (JP)
Developer: HAL Laboratories

Number 5: Super Mario Sunshine
First Released: July 19, 2002 (JP)
Developer: Nintendo EAD

Number 4: Legend of Zelda: Twilight Princess
First Released: December 2, 2006 (JP)
Developer: Nintendo EAD

Number 3: Metroid Prime
First Released: November 17, 2002 (NA)
Developer: Retro

Number 2: Paper Mario: The Thousand-Year Door 
First Released: July 22, 2004 (JP)
Developer: Intelligent Games

Number 1: Legend of Zelda: The Wind Waker
First Released: December 13, 2002 (JP)
Developer: Nintendo EAD 

By:
Giuliano V.
Matteo C.
Justin D.

SPECIAL NOTE: Giuliano believes that Twilight Princess and The Wind Waker should be reversed on the list, with Twilight Princess being #1 and Wind Waker being #4.