BioShock: main story about 7.9 hours; story with some extras about 15.8 hours; 100% completion about 25.8 hours. These are IGDB player-submitted averages from 18 submissions, not a deadline or a prediction of your pace.
Source: IGDB player submissions
Community playtime data is not available for BioShock yet.
Game Tales keeps what happened between you and a game in one Tale you can keep building.