TV-style replays with dynamic panning and tracking shots.
New weather effects (such as rain), car effects (such as headlights), and environmental effects (such as shimmering streetlights).
Improved graphics and track detail, physics engine, and sound effects (better downshifting sounds, for example) yield a more enjoyable and realistic driving experience.
Addictive, new "Drift Combo" minigame -- go for the most consecutive powerslides/drifts to unlock additional cars and courses.
New voices have been added (GT Advance 1 didn't have any).
Differences between US and original Japanese version: 2 players (via link cable both need a copy of the game to play).