We're halfway during our first campaign and we've won zero missions as the rebels so far. We've had a few close calls but mostly it's a total walk for the Imperial player. Our closest was the mission where the IP gets Vader but even then we lost because Vader doesn't need to interact with Luke, opening the door is enough. After playing Descent 2.0, which was hard but doable, Imperial Assault seems heavily Imperial sided (and don't get me started on the threat doubling cards).