I'm repeating myself, but I think in terms of "project completeness" 4 months is as same as 1 month and is the same as 1 week. If you don't choose your project correctly, no matter how much time is given to you, you may not complete it. Perhaps even the more time is given, the worse it gets - people will tend to choose much bigger projects and less projects will be complete.

However, if we have too much time to compete (say 4 months) and the project has to be open-source, I will seriously reconsider participating myself, because in this time I can make another game instead, which could be of "any kind" (not limited by the rules) and which can be commercial (in overall this gives much bigger reward, no matter what prizes you give here). Besides, the bigger is the time, the more disparity among participats there is - some people have full-time job and will have weekends for doing it, while others will have plenty of time.

P.S. In the title "PGD\'s Annual Gama..." you may want to remove "\"