I liked earlier original L&O which had legal twists that taught me a bit about practical constitutional law. Between that and West Wing, it had a fair chunk covered for me of the civics component of my US naturalization examination. Things like, why you don't let your client show you where they hid the body. But, there hasn't been so much of that since back then, just like Suits started off with some interesting legal twists before it all became drama and silliness.