nice shots.
there'll probably be someone along shortly to give a more precise answer but i'm pretty sure that you get judged on your performance. the idea being... i think... to drift as much as possible around the track with particular emphasis on the ability to be able to "link" corners, that is to drift from one corner into another or something along those lines. i think battle if you can get past your opponent it' good however you can only pass them in corners? not on straights etc.
EDIT: To add further to this i found this at
http://www.drift411.com
Today, drifting is an organized competition, with drivers piloting rear-wheel-drive cars to see who can keep sliding sideways the longest. Winners in drifting competitions are judged on the angle, line, speed and show factor of the drift.
“Angle” is the angle the car takes around the track; the more the rear end hangs out, the better. “Line” refers to taking the correct line around the track and is usually determined beforehand by the judges. “Speed” consists of the car’s speed entering, going through and exiting a turn. “Show factor” actually is judged by a variety of factors, such as the amount of tire smoke, closeness of the car to the wall and reaction of the crowd.