Final Fantasy Crystal Chronicles. It came out around eight years ago, but it's my favorite video game of all time.
Why? Because of how elegantly it's made. Not only are the graphics better than just about any GameCube game I've ever seen (and most next-gen games), it has smooth gameplay, genuine challenge, and a great story to back it all up.
The game never took off because it required so much peripheral equipment. In order to play the game, all you need is the basics. But if you want to do well on the game, you need a GameBoy Advance and a connector cable (and a DS won't work). And the game is most fun when played with a group, so that means another GBA and another cable for each player. Still, if you have three friends and a GameCube or Wii, it's definitely worth the investment.
The game does not have any follow-up. I say that despite the existence of Final Fantasy Crystal Chronicles: Ring of Fates, Echoes of Time, My Life as a King, My Life as a Darklord, and The Crystal Bearers. Those games fundamentally altered the gameplay, turning it into a stereotypical platformer rather than the unique RPG-adventure blend that made the first game great. Do not buy them; they range from "atrocious" to "middling".
Still, the original game provides many hours of adventuring fun for one to four players (four players is recommended).