Music is pretty hard to judge if you don't give any specifics. Suppose you have two entries, one is Melodic Hard Trance and the other is Orchestral Gamesoundtrack. You can't compare the two. In no possible way. These two are simply two different routes in music art and what may be amazing in orcgsound does not exist in MHT that has its own amaizing elemenets incomparable with Orchgsound. Also, a person judging such open contest is supposed to know and understand entire music developement and lore.
In my opinion, you should either or both of the two things:
Make a rule that you can use only orchestra (refference: complete midi set without synth and electro drums) and/or split the entries into basic: Core Electronica/Orchestral Compositions/Soundscape, where Core Electronica counds for Trance, Techno, Goa, House, IDM, Nu Skul Beats, Rap Beat, DnB, etc, Orchestral Compositions is obvious, and Soundscape counts for experimental, soundscape, ambiental, envrionmental symphonic. I excluded genres regarding guitars (metal/rock/country...) because I'm not sure how many will go for it...