As I said in my first impression of Dexter, I was a little underwhelmed by the way it started. I had expected great things and they were not immediately forthcoming. Now, at the end of the first season I can say I right at the start.
The whole thing is ridiculous, more a mix of a sitcom and a soap opera than the drama I had been hoping for. The storylines can be pretty absurd and some of the acting is just plain awful, yet for some reason it remains compelling.
Fundamentally, I believe this is because the idea itself is actually a good and the writing, whilst not consistently the best, is pretty good.
The finale of the season arc was a good one, though it does require a completely new one for the second season. It would be a bit much if a second serial killer came and took his place.
The biggest concern at the moment however is that after one season it is already pretty absurd. They are currently up to season eight. If they have made it that far without descending into farce or parody I would be very surprised. Still, that is a long, long way away from now.
Regardless, after one silly season I have enjoyed it sufficiently to move on to season two. The ideas it touches upon (philosophical, religious, moral), are enough to keep my interest. Hopefully it will find its feet and become the really great show I had hoped for.