I'm not sure who the voice actor is, but I love her accent, and she does a great job adapting her voice over the course of Lara's journey from innocent girl to confident explorer. I remember the developers saying they wanted to focus more on Lara's face instead of her "assets," but the voice is also what really nails it for me. I can tell they put a lot of effort into making Lara seem human, unlike the trend for some heroes to remain emotionless/quiet, like Gordon Freeman, or some Call of Duty games.
After having just played Bioshock: Infinite and never getting to appreciate what Frank DeWitt looks like other than on the cover and promotional art, it's nice to see a hero in Lara we can visualize, listen, and relate to.
Everytime I hear her voice, I want to hug her and tease her.