Dexter is such a fascinating TV character. Probably one of the most developed characters that I can't get enough of. Why? Well I'll attempt to pin it down here.
In a nutshell, he's a serial killer that lives by a moral code that sets parameters around who he murders. In a sense, the murders are justified as taking out the garbage that the law was remiss in carrying out. Quite simply, the law can't always be 100% effective in fighting crime.
It's the way he knows what emotional portrayal he needs to convey - whether it's the personal relationship he has with his sister Deb, or his girlfriend and eventually his wife Rita, her kids, or Doakes, who has huge suspicions about the real Dexter. Dexter is able to know what he needs to convey, recognizes that he'll need some external help in conveying it, and will deliver. He treats his social skills no differently than his knife of choice and his weapons. Whereas his murder weapons are always clean, sharp, and ready for its next use, his interpersonal skills are blunted, elementary, but that's his hardship. Most people would not recognize their shortcomings and work on them so assiduously. Dexter is ... different. But of course, sometimes he stumbles and falls short of delivering the emotional oomph required. He learns. As a blood spatter analyst, he's impeccable with details - so he will not make the same mistake again.
He is a master of psychology, but ironically, he can not apply it intuitively for his own relationships. It's a work in progress, and he always strives to feel more, to stretch himself, and to never let his barriers prevent him from living a life of 'meaning'. He spends his life believing he can learn meaning. :)
This show and his character is a perfect blend of a thriller and something raw. It's cutting edge because it always makes me feel alive - to ask the most fundamental questions and to evoke these inquiries brings me back to my humanity. Wow, the irony. A show about killing brings me to think about living. :)