I think people just plan for too much - they see they have two months, and create an epic 5-map entry based on that time, forgetting that in reality, you cannot do that many maps in the allocated time.
I personally judge on quality of mapping, not quantity. A single, small map with zero gameplay is just as likely to win as a huge singleplayer mini-campaign with custom models and voice acting.
Direct your attention to
Deathan's entry in compo 25. This was a small map with excellent architecture and atmosphere, which stood out from other (larger and more complex) maps as the best entry. If you concentrate your efforts on making one excellent map, rather than 5 mediocre maps, you have a much better chance of winning.