Operation Overwatch has squads aim for a successful extraction on any difficulty where at least one player involved is using an Earth Pack character. Meanwhile, the allied goal is to extract 800,000 players in total, with each living player at the end of a round counting toward that goal. The usual split of Commendation and Victory packs will be granted upon squad and allied success (respectively), although Overwatch's Victory pack will grant a new Earth character.
Since the forces of the Systems Alliance failed miserably at Operation Broadside, extraction time during Overwatch has been increased. Listen, extraction isn't a complicated thing. The circle appears, you and the squad stand in the circle until the timer runs out. Don't go running around, don't go looking for aliens, just chill and wait it out. This is why we can't have nice wars.