To me, IMO, I think Lucas can do many things well, and many things he does not do well. Unfortunately on the prequels, he tried to do everything, and his flaws showed in all of the films.
Lucas, is very good storyteller. To me the six movies in Star Wars are all interesting. He definitely has a great imagination, and has created a whole universe on his own. He is very good at pushing technology as far as it goes. The special effects in every Star Wars movie are better. He definitely knows what he wants when he is trying to achieve something. As much as I hate Jar Jar Binks, and I really hate him, he was the first all CG character, which was a wonderful achievement at the time.
The things Lucas is not very good at is: Writing dialogue. In the originals, he wrote the story and had someone like Lawrence Kasdan and Leigh Brackett wrote the screenplay. He is not very good at getting great performances out of the actors. He is an editor, not a director. If you look at ESB, Kershner did a great job because he got the best performances out of Ford, Hamill, and Fisher.
Now most people will argue, "Lucas wrote and directed the original Star Wars, how do you answer that?" True, but that movie was lightning in a bottle. It is a classic that changed movies. To me it is one of the things that everything went right, and a great movie came from it. I think Lucas deserves most of the credit, but as you see the others movies from Star Wars, you begin to see his flaws. Johnathen Demme did Silence of the Lambs, Andrew Davis did The Fugitive, and Kevin Costner did Dancing With Wolves, and they were all classic movies, but they never topped that again, but that doesnt' mean they are horrible directors, lightning struck once where everything went right, and the movie was a classic.
To me the original Star Wars and Empire Stikes Back are the only truly classic Star Wars movies. I think they are because they had the most collaboration. Gary Kurtz was the producer, can you see Kurtz letting Jar Jar ruining the first 40 minutes of The Phantom Menace, he would have said to George this guy is ridiculous. Lucas had Lawrence Kasdan write ESB, and Irvin Kershner direct it. This led to many other ideas to make a Star Wars movie great. Kershner said once that Lucas did not like Han Solo saying to Leia, "I know" but he fought to keep it in and now it is a classic line.
After ESB, ROTJ was downfall of great Star Wars movies. The other 4 are all good in their own way, and I can still watch them endless just because they are Star Wars, but everytime I watch ROTJ, TPM, AOTC, and ROTS, I say, "Damn if he would have done this and this different, man this would be a great movie. " I also think that Lucas started to cater too much to kids. The ewoks, Jar Jar, C-3PO' head making jokes during the clone wars of AOTC! Everytime I watch ANH & ESB I think they are perfect, and wouldn't change a thing.
My point is that Lucas tried to do everything on the prequels, and by parting ways with Kurtz after ESB, he began to the era of more "yes men."
Just watch TPM documentary on DVD and watch how everyone is afraid to give an opinion after they watch a rough cut. The only one who questions him is Ben Burtt from the original crew. Sometimes you need other input, because no one is right 100% of time.
I love George Lucas and respect him alot for giving us 6 Star Wars movies to watch for the rest of our lives, but calling him lucky it too strong. He deserves credit for many things, and deserves criticism for other things. The one regret I have about the saga, is if he stuck with the original crew of Kurtz, Kasdan, and partially Kershner, how much better the movies would have been after ESB. Oh Well.....