I just played it twice. Imperials won both times, Vader is a hoss.
The first game the Stormtroopers never got a marker, Vader just raged right through the map, choking and lightsabering all the way to Leia. He killed her with his last order marker on turn 4. Vader had 2 wounds from all the sustained rebel blaster fire he ran through. He took out almost all of the rebels along the way.
Game two played a little different, with the Stormtroopers clearing a way for the Sith lord. Leia also came out and gave her bonus to some of the soldiers. The stormtroopers got a lot of hits and the rebels weren't defending well. They had to pull back and make a cluster around Leia. A few Stormtroopers got choked, because Darth Vader was slowly rolling down the battlefield behind them. During the fourth round, the rebels had almost wiped out the Stormtroopers, but their lines were broken and Darth Vader gained adjacency to Leia, dashing her plans to run and gun back to the start zone. It didn't take long for the lightsaber to finish her off, despite the Force Intuition power.
I'm going to do more of these as I play through the scenarios. I think I'm going to do the detention block next.