Players each choose a character from the cast of the television series. Each player, on his or her turn:
1. Draws skill cards (which double as action cards),
2. Optionally moves to location on Galactica (or Colonial One, or, as a pilot, through the space around Galactica),
3. Activates a location or plays an action on a card (or, as a pilot in a Viper, moves again or fires at Cyclon raiders and basestars in order to protect the human fleet),
4. Draws and resolves a Crisis Card.
Most crisis cards depict a distressing event (with art and text from the television series), be it a food shortage or a lost scouting party, and offer a choice and/or a skill check to be made to minimize the damage to Galactica or her resources. Skill checks are resolved by players secretly contributing positive (matching color/type) or negative (incorrect color/type) skill cards. In addition, many of these crisis cards also activate enemy ships or move the Galactica closer to making its next jump.
But all that would just make for a typical cooperative game. Each player also receives a secret loyalty card that indicates whether they are a treacherous Cylon (skinjob) or a human. The humans attempt to survive the journey to Kobol (by making jumps that total at least eight units, plus one additional jump to end the game) whereas the Cylons do their best to sabatoge the human effort, either covertly (which involves a great deal of bluffing and secretly tipping the scales via secretly played cards) or overtly (by revealing themselves as Cylons and just hammering at the Galactica with all the tools a revealed Cylon has). Furthermore, halfway through the game another set of loyalty cards is dealt, such that there are a total of two Cyclon players (in a five player game; the number of Cylons and sympathizers varies based on the number of players).
All I'm saying is, it's a good thing Galley Brother B.J. lives on the other side of the country.