They were all fascinating, apart from the one on morphing.
There's another documentary series out which tells the same story - Icons Unearthed: Star Wars.
I watched the first four episodes, because after that it moves onto the Prequels.
This one has the interesting perspective that it features new interviews with Marcia Lucas, who often gets overlooked yet played such an important role in keeping things on track, and making Star Wars the force it became with her skills in editing.