I know a Chabad rabbi who holds cholov yisrael and gets frozen milk shipped to him from the U.S. If after the expiration date, you can consume is for about 2 days after thawing. Seems like a short amount of time.
Anything other than non-fat milk (skim milk) will be adversely affected by freezing — the fat sort of congeals. With non-fat milk, it should be as good as fresh, with about the same shelf life after thawing. When we lived in a community where the cholov yisrael milk came in once a week, we used to freeze it.