From this statement, I strongly suspect you don't actually watch Dexter, do you?Me personally? I hate Dexter. I hate how flawed our heroes are, how corrupt our role models have become. Sure, this may mirror real life. But that's not entertainment to me. Dark, crazy and immoral does not equal complex to me. People throw out the cure-all term "sophisticated", but most times it seems they don't really know what that means, it simply makes them feel better about what they're arguing and that word alone should end the debate, so it's thrown out there. "My show is more sophisticated, I don't know how, it just is, next topic."

Otherwise, you'd know that one point of the story is to argue that Dexter is actually more moral than many of the supposedly normal people around him. For one thing, Dexter actually thinks about morality, which hardly anyone in the show besides him ever does (or in real life for that matter.) The series asks whether striving for the normal good things in life, such as protecting his family, can result in horrible things happening, just as easily as if he were unredeemably bad? Dexter isn't amoral. He has his own morality. The series is a dissection of morality itself.
Why not name a few shows from that period that are as sophisticated as contemporary serial dramas? I'm curious to take a look at some of them.
I'd like to know what these amazing shows are, too. I know a few: The Honeymooners, The Twilight Zone, TOS, maybe some episodes of The Outer Limits. I've also heard that early seasons of Gunsmoke were quite good and not at all standard-Westerns-hokey. But none of those were serialized.