No, he didn't. Lawrence Kasdan wrote 5 and 6. Lucas did do the story (not the screenplay) for all three, and wrote 4, and co-wrote 6. However, he didn't touch the screenplay for 5, which is usually considered the best of the series. Lucas gets a lot more credit than he deserves. Read number 5: http://www.cracked.com/article_19576_6-pop-culture-visionaries-who-get-too-much-credit.html

I'm going to defend the prequels, because most of their defenders seem to have a more of a fleeting acquaintance with grammar, rather than a well-founded relationship. This is not meant to flame them, merely to say that it reflects poorly on the defenders of the prequel trilogy. I also recognize that this means this is likely to be riddled with errors, since I have tempted fate. First, let me provide the mandatory "The original trilogy was better" comment. Do we all understand that now? Okay, cool, we can move on. I can recognize a lot of the bad things about the prequels. The most obvious of which is Jar Jar Binks. He's annoying and slightly racist. I can handle him alright because I was ten when Phantom Menace came out, and as a ten year old, I thought he was awesome. However, the biggest thing that's wrong about Jar Jar is that it shows that George Lucas forgot that R2-D2 and C-3PO were his comic relief. As bad as Jar Jar is, though, Lucas made up for it by making him cause the rise of the Empire. We can all blame Jar Jar Binks for the years of oppression in the galaxy. Then there's the acting. However, I don't think this should be separated from the writing. Hayden Christensen and Natalie Portman give mediocre performances, but they're not awful (Jake Lloyd was awful, but he was also a kid, so that's to be expected). The dialogue is also pretty mediocre, but I don't think it's awful. However, combine the acting and the writing, and it comes off as pretty bad. Of course, whether the acting and writing are mediocre or awful is subjective, and that's just my opinion. Another big complaint I'm seeing is that it turned Darth Vader into a whiny little kid that didn't match how we imagined him when all that existed was the original trilogy. I understand the frustration here, but I don't see it as a legitimate argument as to why the prequels are bad, in and of themselves. It was never up to any of us what Darth Vader was like as a kid. Now, unfortunately, it was up to George Lucas, rather than any of the other writers or directors who worked on the original trilogy, but still, not up to us. "It's not as cool as how I imagined it" isn't legitimate because it was never our job to imagine it. Frustration aside, we should judge the movies in and of themselves. The prequels also create more plot holes, and I fully recognize that as a problem. Anyway, I think my ultimate point is that the prequels aren't as bad as people say they are, and, of course, that anyone who says that Revenge of the Sith isn't awesome is lying. In fact... http://www.rottentomatoes.com/m/star_wars_3/ Compare to... http://www.rottentomatoes.com/m/return_of_the_jedi/ Of course, that means very little. Just an interesting little point.