The PAL version features a number of improvements originally intended for the NTSC-U version.
Penta Penguin, the secret character unlocked by a cheat, is unfinished in the NTSC-U version, but the later release date for the PAL version let the developers finish him and fix a few goofs.
The icon for Penta's mask no longer shows Uka Uka instead of Aku Aku. All of his placeholder voice clips (such as "Penguin yay 1") were replaced by the final ones. Most notably, Penta's stats are no longer the same as Polar's and Pura's - they are now maxed out in every category, making him the best racer in the game.
Location, Location, Location
The name for each hub in Adventure mode now appears at the bottom of the screen whenever you enter it.
The default high scores for Time Trials no longer display 9:59:99, and now have actual times for each track.
The scrapbook was shortened considerably. There are a lot less pictures and no fading transition between them. The Japanese merchandise was omitted entirely. This was done to save space, as the PAL version of the game just barely fits in one disc due to the multiple languages.