Participation on part of the recipient / user of video games in terms of adding content (e.g. mapping) to or changing content (e.g. modding) of an original game is an interesting phenomenon of today's popular culture. The developers in the meantime reacted to fan-made material that made their games live and sell for a longer time by making it more comfortable to edit games e.g. by providing user-friendly level editors, tutorials and SDKs. Now what makes modding so special?
From my own experience I would argue that modding most often is a community effort - not only as mod teams split the different fields of work (e.g. graphics, coding, script) among their members, but also because there is a modding community in the www that helps beginners by providing tutorials and feedback. The net further facilitates the distribution of mods to a worldwide audience.
Is modding (partly) a vanguard movement in the field of video game art? I would argue that the advantage of modding on the one hand lies in the (nearly) infinite possibilities of being able to change the whole mood and handling of a game to enable one's own visions without having to program an own game and on the other hand (maybe more important!) in making sure that many people will be interested in one's own creation because the modded games most of the time are the popular ones. One therefore in an idealistic view could say that modding fosters creativity and in some cases may make it easier to explore new ways of gameplay (as for example in the "Dystopia" - mod), because it can take such risks due to it's non-commercial nature while on the other side having an wide audience guaranteed as even experimental mods (most often) are tied to popular video games. Can video game companies not only find new talent among modders but also new ways of gaming (tested and approved by an audience that played the experimental mods)?!
Looking forward to read what you make of my soapy thoughts ;)! (hope the spelling errors aren't that bad, but English isn't my native tongue >_<...)