I know that currently most people rate Heroes as the best piece of television out there. But if I'm honest I have to disagree. Heroes is good; I enjoy it greatly. But it's not the best.
The problem I have with Heroes is it doesn't challenge the viewer so much. While there are mysteries and strange occurances in the show, it's no more unusual in this than many other Sci-Fi shows. It also tends to make giant leaps of logic and provided a rather weak season finale. All of this said, I enjoy watching Heroes immensely. Sylar remains amongst one of my favourite characters of all time and the current plot seems seriously exciting.

But I personally feel the show pales in comparison to Dexter. Dexter came out last year and I was immediately interested due to the choice of lead. Michael C. Hall's performance in Six Feet Under was magneticly powerful, so I was immediately interested in seeing how he'd manage to play such a very different character. As I read about the show I began to feel excited, it was a show that pushed into an unusual field of television. Placing the lead character in the role of a serial killer is a bold move, especially in television. Books (where Dexter originated) can contain much darker characters as it's not so bad to marginalise the audience. Television shows on the other hand cost a huge amount in resources and time. So to commit to such a dark subject matter was a brave move by Showtime. (Showtime, you're forgiven for the loss of 'Dead Like Me'!)

Dexter is not a show for everyone. It's exceedingly dark and disturbed, the average viewer prefers not to have themselves challenged by the show they're watching. They like their whites white and blacks black, no shades of grey. Dexter does not provide this, instead it asks the viewer a very hard question. "Is a monster who preys exclusively on other monsters acceptable?" "Is it OK to kill if it protects the innocent?". Additionally confounding this issue is the sublime performance of Michael as Dexter, the novel provides a very dark but humourous vision of Dexter. You understand his needs, his drives, his reasonings and also his humour. Michael brings all of that to his performance and more. He dares you to like him, and you do. Even when you see the horrible things he does, you still like him.

The first season more or less followed the plot of 'Darkly Dreaming Dexter' but with additional material used to expand and enrich Dexter's life. It does deviate in a few key points, but I'd still recommend watching the show before reading. I found that to be the more enjoyable way to experience the show. But others have disagreed and prefered the book.
In a spoiler free version, the first season introduces us to Dexter, allows us to experience his life and understand "Harry's Code" the code of rules that Dexter follows strictly when killing his victims. A code created by his stepfather to protect and control Dexter's urges even after Harry's end. But Harry's life becomes disturbed when another serial killer moves into the area. A killer who takes an interest in Dexter...

The season was a whiteknuckle ride from the first episode to the end. A total tour de force in every aspect. It did not disappoint at any moment. From the very first moment I watched the opening credits in each episode I was hooked.

The second season has managed this and more. Dexter is in such a precarious position, society would not, could not accept him. And without spoilering anything too much, I've been sat on the edge of my seat genuinely scared for Dexter.

I'm actually worried about a fictional serial killer's life and problems. That's how good this show is.