For better or for worse, they tried to paint him as merely being a highly confused and slightly paranoid person who made a decisions that led him down an unexpected path. In doing so, the character kind of didn't often take on the stong personality that is Darth Vader. At the end he finally started to show signs of being a person who is actually evil. He finally started to display more than just mere confusion and discontentment. His actions finally became more treacherous, and his attitude more flippant and disloyal. But it probably would have been better if that started happening sooner.