A Rising Darkness: the mayor and Jack have formed an alliance, and are attempting to take control of the city. This is a war fought in the shadows, that the players might not even be aware of at the time. The first phase was to raise a dracolich and use it to destroy the cathedral, killing the Abbot and ousting the Templars from power. Next, they must take on the thieves' guild and the wererats. Fiinally, they intend to raise an army to expand their dominion. Eventually, the characters will be powerful enough to confront the mayor, learn about Jack (the secret power behind the throne) and end the reign of terror. However, in the meantime the party is likely to face many defeats and setbacks if they attempt to interfere.
The plight of the common man: at low level, not much separates the party from the average peasant. These are dangerous times, when human civilization hangs on by a thread. The populace is largely subject to the whims and conflicts of the powerful, and preyed upon by monsters and villains. I want the players to be aware of their characters' limitations, choose their fights carefully, and try to keep a low profile lest they get trodden on. It is important for them to try and gain allies, so that they don't stand alone in a hostile world.
The major risk I see with the above concept is that it will become very frustrating for the players if they feel that their characters are entirely ineffectual. It will be important to mix in subplots where the party deals with the less epic concerns of the hoi palloi - only 10% of encounters are supposed to be "overpowering". However, the idea is to have a noticeable contrast between the way the characters are treated as they rise in levels. I'd like them to have a sense of achievement when they attain greater power and become a force to be reckoned with.
My goal in the early game is to introduce some of the factions of the city - I want to give the impression of a living community, with many conflicting goals. The characters will make many enemies (but hopefully also some allies). It will not be unusual for people to react negatively or with suspicion, since the frontier is full of those who prey on the weak.
I'd like the players to decide what their characters want for themselves, and then go after it. I need to make sure I have given them enough information to do that. I want to run a freeform adventure, and be open to the possibilities of collaborative storytelling and world creation.
Some things that I assumed from my experience with past adventures