After exhaustive research into many of the Mode-7 kart racers for the GBA, and playing through their campaign modes, I can say with authority that Crazy Frog is the worst Mascot Kart Racer for the GBA, and probably All Time. It isn't even bad in an interesting way.
You can't drift
There are 7 other characters, besides the Crazy Frog, who are in this game. It's unclear where they fit in the Crazy Frog Cinematic Universe.
There are only 5 tracks. Five total for the whole game.
Think about what this game is about, a ringtone mascot, who's whole deal was being annoying. Crazy Frog was everywhere but nobody liked him. Crazy Frog Racer for the GBA is a part of the cultural debris, washed up upon the Content Shores.
There are other platforms I haven't explored and certainly there may be worse racing games out there, but from my point of view, this is the worst one.