I thought it was fairly nice how they did that. It's different from later games where it's "Oh no's I was bad; now I'm good. Let's go save puppy dogs and christmas everybody!!!"
Instead Leon was a more unigue character, and was a good person who then got lost in the opportunity for power. Which he took, even at the cost of many other people's lives. One thing I did enjoy about his character that he wasn't exactly the good guy, but at the same time he wasn't a true villian either. He was more in the middle and made it a bit nifty to have him in your party.
