Not surprised about the slavers comment - read his commentary on trying to make Red Tails and how he couldn't even get a studio to do it because it had (vast majority) black protagonists. (Story about the Tuskegee Airmen).
The best part of all of this is you get to hear all the "Lucas is racist" commentary...except this is a dude who spent his own money trying to push representation in film long before it became a talking point and a way to try to sell things.
Lucas covered the cost of production with his own money, and provided a further $35 million for distribution. In an interview on The Daily Show on January 9, 2012, Lucas stated that the long delay in the production of the film was because major film studios balked at financing and marketing a film with an "all-black" cast and "no major white roles." He went on to explain that studios receive "60% of their profit" from overseas, and the studios feel there is no market there for films with all-black casts. Red Tails is also the last film Lucasfilm made independently before being acquired by The Walt Disney Company on October 30, 2012.
As for selling Lucasfilm - he wanted to retire and he turned around the day after he sold it and donated all the money he got from the sale - so he didn't do it for the money. (Dude's hella rich and a hippie)
Even as someone who freaking loves TFA (seen it 3x, hope to see it 3x more at least) - it is a re-boot of ANH in 2015 ultimately. Had the prequels not lowered expectations so badly for those who grew up on the original trilogy; it would have been received far, far worse.
People keep on mentioning the money, but he didn't even sell it for the money. The money that was asked for the property was a sum to all go to charity. The 4 Billion figure (I think it was less than that though around 3.5-38 Billion) was considered among anyone with a notion of property value as a ridiculous deal. No one in there right mind would sell a property like Star Wars for that amount. It's a bargain, especially for a powerful company like Disney. It was chump change to the max.
And that right there should tell you how crazy George Lucas really is.
I believe when the deal was made, the value for Lucasfilm was in the 16-20 billion dollar range.
He's not wrong. The problem the prequels had is that no one helped him out. He wrote and directed every single one, unlike the original trilogy. He also was surrounded by yes men who basically didn't question anything he wanted to do or input ideas of their own. It's easy to not see the forest from the trees at that point.
The prequels in concept aren't a bad idea. The overall narrative and character themes presented are good. They're creative. And they make sense. The problem is the execution of those concepts. Lucas is good at ideas but he can't really write. That's why the dialogue is extremely poor. He cast some great actors and they did they best they could, but it's hard to save a poor script. I think with another writer cleaning up the scripts and someone else involved in making creative decisions (along with him) the prequels would have been much better.
They had a lot of creative ideas. From what has gone around on the Internet my understanding is that Lucas asked around for others writers and directors but no one wanted to help him bring his vision of the prequels to life. Probably due to the pressure of Star Wars being this huge "important" franchise. It's a shame that no one helped him out, because I think that's really all he needed.
Look at the Clone Wars TV series. Same exact thing. Lucas came up with a lot of concepts for that show, was heavily involved in the creative decisions all through the end. But he had a talented team of writers working on the scripts and Dave Filoni leading the thrust of the project. And the series turned out great. I think this is what Lucas needed on the Prequels.
I sort of wonder why he didn't consider retaining ownership of the property but allowing Disney to make and profit off of his ideas. From what we know of him, that seems like it would have been the best solution. I also imagine that Disney would have jumped at that in a heartbeat also.
He wanted to retire, primarily, and do indy stuff without much press or oversight. As for the pre-quels; I think you hit the nail on the head. If you ever get a chance to read the Rinzler books on the making of ANH / ESB / ROTJ - you can a) see where Disney copped a TON of his original ANH ideas, including Luke/Leia being a combined character and a woman and Han being a black male ex-stormtrooper (and no Obi-Wan ish character) and b) how he freaking HATED having to write ANH. He loves being an editor and an oversight guy, but he hated writing ANH when he had to.