Splitting the Difference in Creating Characters

I think that creating characters with a unique, engaging voice and point of view on the world is the essence of great writing. I've seen some writers with an affinity for plot, who don't have anything to say through their characters, and the stories feel flat. It's sort of like making films--just because a person is technically proficient, it doesn't mean that they have something amazing to say. Teaching film students, I find that the students who take risks conceptually are the ones whose ideas really strike a chord. This is true, I believe, of the professionals, too. So, I've always asked myself, how do I push my characters to the extreme limit, making them as engaging as possible? See, in the beginning, when I was learning to write, I think that sometimes my characters were way over the top and my plots were an absolute mess. A few managers said that I had an interesting voice, and that they would read more of my work, but the plots were simply confusing. Fast forward to a few years later, I've really been studying the craft of plotting and working very hard to understand story flow and logic. But now, I think what's happened is that I've lost some of that voice that used to be in my early scripts. A teacher of mine read one of my recent scripts said, it's all plot, what happened to those amazing characters of yours? If this had been a few years ago, I would have been pretty depressed (he also said it was the worst thing I had ever written, but that's a different story), but I took a couple weeks off and really pondered this question of character. I've been racking my brains a bit, trying to really think about this question of character--what is the essence of a character, and how do I, as a writer really make that shine. Sure, I do a character bio, I spent time figuring out motivation and all of those things. Finally, after some days of thinking about it, and developing some character charts that break down things like inner and outer needs, I sat down to write and I realized something. Creating characters for me is about instinct. I had a teacher of mine who would always say that writing with all instinct is extremely dangerous because when you're stuck, you don't know how to fix things. I get that, but for me, I realize that I have to get to a place where I am thinking through the logic of the plot, and the character's relationship to plot, but then when it come to creating the essence of the characters, I have to use my instinct and deeper understanding of who I think people are and how they work. I've gone back and revised this script, and I realize that I've found the voice of the main character through this process. Sure, I'll go back and revise, revise and revise, but I think this method of creating characters through my own experience is something that works for me.