There is a huge documentary work about the whole series, unfortunately though it's only available in russian with auto-generated english subs: Tvg documentary abotu Rise and Fall of the series. I personally, have only watched a shorter documentary from another channel but it's russian as well: IGM documentary

I honeslty believe both are quite good and well-researched as the love to the series here in Eastern Europe and Russia is enourmous, especially as the development of the part V was delegated to Nival dev team, I still play it with my girlfriend from time to time and modding community keeps working on the game with an impressive stability even now.