Edward Norton didn't get a hair transplant until after his roll in American History X. His hairline was noticeably thinning around the temporal peaks as well as the top of his scalp. He decided to nip the problem in the bud by getting his hairline straightened and the top filled in. Quite frankly, it looks unnatural because very few people have a hairline that's that straight. People usually have to shave their widows people a bit to achieve a pencil line straight hairline like that.
This before and after montage shows Edward Norton's hairline at different stages of his life. Overall, the hair transplant gave him a full head of hair with no noticeable recession. His forehead is a little big, but that's how it naturally is.