I have to disagree utterly with DreamGuy's assertion that use of non-influential main characters is indicative of poor writing. Read any great fictional works of the last two millenia. There are always greater powers at work in the world of the characters. That the characters are able to cope with, strive against, and sometimes succeed is what makes them interesting, and in turn, the writing good. Example: The Odyssey. Odysseus, neither the strongest nor the most kalos of the Greeks, uses his resourceful mind to contend with the anger of gods and foes much greater than him. Heck, if you want a contemporary example, how about Harry Potter? The main characters in those stories are students, getting by in a world populated by wizards much more powerful and fearsome.
If anything, when characters become great movers and shakers, writing becomes abominable. Why? Authors in those cases are incapable of sustaining the level of detail necessary to make their stories realistic because such levels of power/understanding of government/world functions and motivations are beyond the scope of their imagination/comprehension. What results is a story that falls flat. Read Eddings' Belgariad/Mallorean series, for example - certainly entertaining, fluffy fantasy romps, but with few exceptions, the main party of super-world-shakingly powerful characters never face a real or interesting challenge. What results is a ten-book-spanning yawn of a story. Reread Dune, if you haven't read it in a while. Would rulers of *entire planets* behave the way those characters do? Heck, look to the abortion that Robert Jordan's series has become - progress in that story line has ground to a halt due to his geo-political twittering.
Good storytelling requires compelling, not necessarily influential, characters. In my opinion, the best storytelling occurs when much of the rest of the background remains concealed (and provided that the background does, in fact, exist) - the tip of the iceberg metaphor. It's what made Tolkein's work great, and was what made the Matrix great, until we found out there was no decent "rest of the iceberg."
As for the linearity/non-linearity argument, I think it's strictly a matter of opinion. As for people complaining about the scenarios, why are you wasting your time playing this game? Why don't you write your own scenario and show everyone how it's done?