Atonality can be heard all throughout the six SW scores. The OT, especially after the first score (which is the most traditional, in the Korngoldian/Golden Age sense of the bunch). There are plenty of wonderful avant-garde moments in ESB and ROTJ, but as Lee mentions, done in a more subtle fashion to create supporting atmosphere or other varying textures, the flashy melodies are still at the centre of the whole thing. And it seems what Lee was referring to as "atonal", correct me if I'm wrong, was the more aggressive nature of it, where sometimes those modern elements take the centre stage over the more traditional melodicism. There is a certain lack of focus, or a core element that ties it all together in the later prequel scores, so you end up with wonderful vignettes in the work, but only loosely tied together by "transitional" material that doesn't sound like it was exactly written with Williams full heart into it. With the OT, Williams struck a nice balance between the modern and the traditional, so much so that guys like KM get to have all the fun they want with their fanfares and themes while others like Sharky can enjoy the more fascinating textural elements Williams employs throughout the underscore.