decent, but...
I like racing games. So, this is an easy win for you. But since I got all the track medals except for the two "legendary", the game keeps crashing once I finish a track. Last crash on Ice age with 45.57, so, I wonder whether it is some bug or some problem on my end.
Besides that: If s/o sets the ultimate time for a course, will the legend and legendary medal be non available any longer? As for keeping highscores, it's fine, but for the gameplay, that's rather a no go.
I think you're menu design needs some polishing and there should be more courses and/or game modes (time attack, highscores for different car types, more unlockable upgrades, ...)
Come on! Make this an epic racer, it's got some potential.