It should be a law- If you own a GCN, you must own Paper Mario: The Thousand Year Door.
Graphics: Slick and clean. The game is absolutely gorgeus. No, you won't get Mario mixed up with your plumber, but they aren't meant to be realistic. Every little effect is awesome. When you activate a switch, you often see the effects come in a page-by-page effect that looks awesome. Screenshots just don't do this game any justice- You have to see it in action to get the fluidity.
Sound- The soundtrack is positively quirky. Some songs are variations of classic Mario tunes; others, surprisingly refreshing pop-type tracks. Not like Brittany Spears pop, but beepity boo bob, remeniscent of the Phendrana Drifts in Metroid Prime. The sound effects are also great- you can even change them with different badges.
Gameplay- Simple, yet deep. If that makes sense, than I'm not the only insane one.
In Battle: You choose basic attacks- Jump or Hammer (more often than not, but there are more). You get an Action Command, where you use buttons to string together attacks or do more damage, and sometimes defend. You also have badges, which give you more varied commands to help combat specific enemies. However, each badge takes of BP and you have a limited amount. You also have FP for your special attacks. You and your partner have HP, and when Mario's HP hits zero it's GAME OVER! The crowd is a new element. The crowd often boosts your Star Power; which lets you use even more uber attacks that you obtain throughout the game. You can appeal to the crowd to get even more. The stage is also effected by attacks- use a ground-shaking POW block and some scenery might fall on your head. The game is deceptively simple and requires reflexes. You level up with star points gained from enemies and you can up your HP, FP, or BP at each level up. Awfully addicting.
Out of Battle- Little puzzles and platforming. Nothing too big. They often involve a special power of your partner. However, Mario gains real paper-like abilities- folding into an airplane, getting skinny to go through tight places, etc.
You'll spend a good 25 hours on this game, especially if you go out of your way to explore everywhere. And you'll want to, because the game is just so much fun.
Story- Peach finds a map to the crystal stars. She writes to Mario to go exploring, but when Mario goes to meet up with her she is nowhere to be found. Mario discovers that the map Peach sent to him with the letter holds the secret to an ancient civilization undergorund, but he needs the crystal stars to get in the Thousand Year Door. He sets off on a journey to meet up with peach and get the Crystal Stars.
General Praise-
If you claim you like games and you own a GCN, you must have Paper Mario: The Thousand Year Door. From it's hilarious diolouge to it's addicting gameplay, this is the definitive RPG on the Gamecube. Everything about the game is just a masterpiece. The ONE flaw is the lack of charm the first one had. However, it's the most solid game on the Gamecube and you can't go wrong with it