Yahoo's Jeff Passan did a story on how the sport is judged. Here are the basics:
Riders are graded on a 1 to 100 scale based on entirely on "overall impression."
The judges are allowed to talk to each other, and the head judge can suggest changes.
The official judging criteria urges judges to consider difficulty, amplitude, execution, variety, progression, and combinations. But there are no objective metrics for those factors. There's no strict definition for which tricks are more difficult than others, or by how much. The official judges manual says "difficulty is very individual" to each rider.
The judging is being conducted by a skiing federation, the FIS, not by snowboarders.