Know that the first two are tied as two of my favorite games of all time. The rest aren't in any particular order.
1. Super Mario Sunshine - Nearly 100%-ed this except for two blue coins I can't find.
2. Sonic Adventure 2: Battle - Completed Last Story. Never planned on doing emblems. Shoutout to chao garden.
3. Animal Crossing - Paid off all debts (with cheats)
4. Paper Mario: The Thousand Year Door - Never started Chapter 8 because I read a walkthrough and got scared; still love it
5. Sonic Mega Collection - My first Sonic game(s), except for that one time I turned on someone's copy of Sonic Chaos
6. Frogger: Ancient Shadow - According to others, this is the best 3D Frogger game. I lucked out.
7. Sonic Adventure DX
8: Sonic Heroes - I think completed everything except for Team Dark's story (and the final boss)
9. Mario Superstar Baseball
10. Sonic Gems Collection - Has some of the best early Sonic soundtracks... except for Sonic CD (I got the American version)
11. Mario Party 6
12. Donkey Konga - Songs from this get stuck in my head sometimes
Honorable Mentions (AKA the remaining Gamecube Games I own)
Tak and the Power of Juju - Honestly I had a lot of fun with this one, but some of the enemy designs scared me, so after a certain point I never picked it back up again. It has probably aged badly LOL
Sims: Bustin' Out - I'm surprised I still own this one. The reason I got into Animal Crossing is because someone saw me playing Sims and thought Animal Crossing would be more age-appropriate.
The Spongebob Squarepants Movie - There was one part I got stuck on and never made it past.
Some Tetris Game - I don't really like Tetris. I think my dad bought this?