The idea of curing a Corruption being the objective of each game session has merit, having a variety of these Corruptions that each not only change the end encounter but also gameplay throughout. Add to that a Trait which colours the corruption and that is heaps of variety. The idea of a campaign instead is still worth exploring, but would mean a different type of interaction between the players at the beginning.
One of the key narrative gameplay elements that may work is assembling and levelling the personal story of your 'party'. Getting a group together that can combat the Corruption but also put aside their animosity for the other side should be fun.
Anyhow, while I work on the details of some of these things, how about a little peek at a few of the interesting board games active on Kickstarter at the moment. Crowdsourcing could be a real boon for board games...
A few pics from Kickstarter as well: