Dave Filoni is the show runner of "Star Wars: The Clone Wars". At the Celebration V panel for the series he right out said that Lucas was their "secret weapon" in terms of generating story ideas or characters. The two of them essentially bounce ideas off of each other but Filoni has full control.
Looking in from the outside, it seems to me that Lucas does generate a lot of concepts, but unlike the PT, where he had nobody who could shape those ideas into a good, strong storyline, he now has Filoni to do that crucial part of the job. The result of course is much better now.
I don't blame Hayden Christiansen at all for the portrayal of Anakin Skywalker in the two prequel movies. I fully blame George Lucas for writing the character as a whiny, unlikeable spoiled brat who thinks the universe revolves around him.
I go back and forth with who's to blame.
On one hand, the character makes sense in the story as a whiny, unlikable spoiled brat, in that there's no other real motivation for him to side with Palps other than being stupid, willful and mad at the world in an adolescent-tantrum sort of way. The problem is not logic so much as the idiocy of expecting us to care about a character like that enough for the story to have the emotional impact it should. The story makes sense, but it's not a story worth telling.
On the other hand, the way Anakin is being written in TCW is a character worth telling a story about. But then there's a big, glaring hole regarding his motivation, since he is neither stupid nor emotionally immature enough that the PT logic still makes sense. The story is worth telling, but no longer holds together logically.
Either way, the story has a huge, fatal problem. The right way to resolve it is to rewrite the character (as is being done) and then revise the story so that it now makes sense for the re-characterization. It's possible this could be accomplished entirely within TCW by setting up an adequate backstory for Anakin's fall, and implying that the situation in ROTS was more a straw-that-broke-the-camel'-back thing.
Either way, the blame ultimately lies with Lucas. If Christensen wasn't capable of playing the role correctly, Lucas is to blame for hiring him. If he didn't understand how to play the role correctly, Lucas is to blame for not directing him better.
Given that the whiny-brat characterization
does make sense in the PT, I suspect that what's really happening is that Lucas did intend to write the character like that and grossly underestimated how much it would sabotage the whole story. Now he's revising his mistake, so at least he realizes where it all went so horribly wrong.