The jam will be rated on 5 criteria :

• theme(how well is the implementation of the theme)
• graphics(how well the graphics are)
• game play(how well the game is to play)
• sound(how great the sound is)
• overall(how great the game is overall)

The  overall winner will be the person who get the most rankings in all these criteria

but there are winners for all the separate criteria

edit: forgot to tell that there is also another one called host's opinion which is basically the host's(mine) opinion about your games which can be ranked only by me