This video was originally going to be an entry to the BIM 2010: Avant-Garde contest. Here's a brief explanation of why it took so long:
All of the footage in this video was filmed before the deadline of the Avant-Garde contest, but we didn't edit it in time. Afterwards, we didn't have any good gun sound effects and we lost interest in the project. A while later though, we watched it and realized it had a lot of cool animation shots that we really liked. So eventually, we finished editing it and this is the final result.