They will judge your map according to three factors: trigger complexity and smoothness, style of map/originality, and fun factor. I guess another prize that is not mentioned is instant fame as a UMS map maker in the UMS map making community.
Currently Staredit is the home of the best UMS map makers in the starcraft community. I have been trying to convince them to set up a team of pro-map makers, so far in vain. Their usual reply is that making pro-maps is not their thing. If it does not have a complex tree of triggers it is simply not a map for them.
Still I am under negotiations with Yoshi da Sniper about the subject. My dream of one decent pro-map per week or month, made by the best map makers and hosted here at GosuGamers will become a reality.
Links
Staredit.net - Source