- "I think I should write a letter to him, telling him, something along the lines of, Dear George Lucas, you are a very talented man, however you can't write dialogue. Please don't ever try to write it again."
- —Kippur, in his LiveJournal.
George Lucas is notable for being somewhat hated by lovers of the canons he created. Most of them are thankful for him making it in the first place... but really wish he would leave it alone. There isn't an amazing amount of controversy around his part in the Indiana Jones canon, although many fans were disappointed with the fourth installment. His position as the creator of Star Wars is a whole other story.
George Lucas wrote and directed the first movie in the classic trilogy (just Star Wars, or A New Hope), but he did not direct the second and third movies (The Empire Strikes Back and Return of the Jedi). Coincidentally, there is a large portion of the fanbase that believe these two movies are the best ones of the run.
These three movies made him incredibly rich and influential. He went on to not take writing or directing aid and create the prequel trilogy. Although the integrity of the prequel trilogy is debated, this act is rather like an influential fiction writer suddenly dismissing their beta or editor... with undebatedly bad results. From a critical perspective, the prequel trilogy is riddled with problems at the very least — to the point of being nearly unbearable to some fans. The romantic scenes, in particular, are awful from not only a critical but a simple audience perspective, and it is the opinion of many that they should never have seen the light of day.
His policy on the Star Wars Expanded Universe is worrying in two different ways:
First, his screening process for letting writers play around in the universe is very loose, and therefore there aren't many books in it which are universally liked (though, inversely, neither are there many which are universally hated, though there does seem to be more bad than good).
Second, Lucas has a tendency to ignore the EU outright when assembling new works, which had some sections of the fandom extremely worried about the speculated thrid trilogy throwing out beloved bits of the EU and replacing them with unsavory and yet very, very canon things. Lucas eventually turned over the reigns for Movies Seven, Eight, and Nine to Disney; ironically, much of the EU is being classified as "Legends" now, and the movies may yet wind up contradictory to what has come before. His position on the EU also makes the nature of Star Wars canon confusing; according to him, the films are the only "real" canon, or at the least the films and EU are two different, mutually exclusive canons. Fans seem to disregard this, but it can make distinguishing what is canon and what is not difficult in the Star Wars continuum.