As I recall from interviews with Kirshner and Kurtz, there was some shooting of scenes that had some special effects shots that were necessary. Not being what Kirshner wanted, he had them reshot to George's dismay. Given George's "its good enough" mantra, I think the finished product is reflected of an attention to detail that might not have otherwise been there had Lucas been at the helm. of course, it is speculation as to whether Empire would have been the same film had George directed. I would tend to think not. Its no newsflash that I do not necessarily think Lucas is a great director in the traditional sense. As a technical director, he probably has no equal. But if he had brought a "two headed monster" to ROTS, I have no doubt it could have been that much better and challenged ANH and ESB as the best.