The idea behind this was good and could have been a very interesting and thought provoking movie, however, it is riddled with inaccuracies, and any information taken from it needs to be taken with a grain of salt.
Part one:
True, many religions do have similarities, and a semi-convincing segment could be done on it using only true facts, and making no assumptions. This however is not it.
The most blatant and one of the most damaging facts to the arguments is that Christ's true birthday is not actually Dec. 25. We celebrate it as that today because the actual birth date of Jesus was lost over the years, and the church decided to celebrate his birthday on that day to coincide with that of some pagen gods, in an attempt to make their religions similar to aid in converting these people.
This fact is one among many that this movie chose to omit, of fabricate in an attempt to deceive the majority of people, who as a whole have very little knowledge of religion.
here is a site that lists similarities between major gods and Jesus. Pick any that appeared in the movie and you are likely to find an inaccuracy. If you don't believe what you see check the citations, they checkout, and are far more reputable than that of zeitgeist.
http://kingdavid8.com/Copycat/Home.html
and more:
http://www.unexplained-mysteries.com/forum/lofiversion/index.php/t98970.html
Part two:
Ok, so we let WWI start, we let WWII start, we let Korea start and we let Vietnam start. Thus we attacked ourselves to start the current war? The only arguments that this part makes are arguments that have been debunked countless times from the loose change videos, and ones that are assumptions at best.
All that this part is is a blatant destruction of the films credibility and i will not wast any more of your or my time on it.
Part three:
Was kinda interesting, however due to the source i kinda doubt that it has any accuracy at all, and if it does then they should have let it stand on its own instead of destroying its credibility with the junk that came before it.
This could have been a damn good movie if they portrayed the first part accurately, ditched the bs that is the second and eliminated any inaccuracies that I'm sure exist in the third. But because they didn't any similar film that comes out in the future will now have an even difficulty proving their case. good job zeitgeist.