what are the changes we can see…
Changes in what? Your network? You server? Your desktops? Your applications? The obvious change will be that you will have Active directory installed where you didn’t have it before. Beyond that, it’s impossible to say without knowing what you had before you installed it.
Maybe it’s a question about the differences between AD 2008 R2 and previous versions? I’d agree that more info is needed before the question can be answered.