So, a little 'old school philosophy' discussion here, or at least a comment so that y'all can get an idea of where I'm coming from with this campaign. This came out of a chat that mdengler and I had recently.
One of the interesting type of comments I see regarding old school modules or campaigns is that the stories told afterwards tend to be as much or more about the setting (the dungeon, the town, the region), than about the characters. A lot of these old school modules/campaigns are "killers" or meat grinders, so characters often die. However, the players enjoyed peeling back the layers of the locale, even if it's with multiple characters each. In effect, the campaign is about the place and the people who uncover its secrets. And the ones that actually become higher level through extended play are truly epic characters as opposed to many more modern campaigns which are character centered and the starting characters are assumed to be the ones which will carry through to the end, and given advantages (and die roll fudges, other GM interventions, etc) so that they can do so. That's not to say that either extreme is bad, I have great fun in some of the real world RPGs I've played in the past few years that fall more into the latter category. And I've seen Story Hours where the DM's goal is to kill (fairly using the rules) his players as often and in entertaining ways as possible using published modules (and his players seem to enjoy the type of game he runs).
While I won't be your 'adversary', my goal is to explore the region with you. I won't make the whole thing a 'meatgrinder', but there may be places within it that are. Characters may (most likely, will) die, but my hope is that uncovering the secrets, and building a shared history of the region will counteract any such occurrences.
And one other note on the subject: As is the case with many sandbox environments, just because someone says something about a Dragon in a cave (as an example), doesn't mean that the DM has a guaranteed way for characters to defeat it at their curent level...

I think everyone understands this, but just making sure it's upfront before things really get going.