Colosseum and/or Gale of Darkness for that amazing soundtrack.
https://www.youtube.com/watch?v=6tHMCGLnchoCrystal Clear in stereo played on Pokemon Stadium 2 is a delicious blend of comfy and kino. Exploring Tohjo with the only barriers being your own choice is an amazing experience that actually warmed me up to the idea of having an open world Pokemon game.
>>36319401This is also an acceptable answer.