Here is the full list of all 12 N+ achievements worth 200 gamerscore. It takes around 15-20 hours to unlock all of the achievements on Xbox 360.
Complete 10 co-op episodes.
Complete 5 co-op episodes.
Win 10 races in ranked online matches.
Complete all 50 Single Player episodes.
Complete 40 Single Player episodes.
Complete 30 Single Player episodes.
Win 10 survival games in ranked online matches.
Die 1000 times in Single Player mode.
Complete 15 Single Player episodes.
Complete an episode without dying in Single Player mode.
Complete an episode and obtain every gold piece in Single Player mode.
Complete one tutorial episode.