This should be in the official rules section. Copied from the facebook comments:

Andrew Wilkes: Are there any tips on what criteria will be influential on what is judged as a winning entry?

Rémi Verschelde: For now I've picked "Theme interpretation", "Gameplay" and "Graphics and sound" as criteria, which would be evaluated separately and also averaged in the "Overall" criterion which defines the jam winner.

Also what will be the reward structure? 1st, 2nd and 3rd in each category, for the total contest, and honorable mentions? Out of 270 registrants, I would think you'd have on the order of 10-15 finalists.