One of my favorite series. Not my personal favorite but high on the list. I really loved mentalist. To me mentalist was a much better all throughout but I haven't completed the whole dexter series yet but I'm well enough into it to know that for me it's been less engaging than mentalist. Overall it's really really good and I'd definitely say it's a must watch. But I'd recommend buying mentalist as well. I've watched the mentalist multiple times and I'm not one to watch even a short movie more than once hardly at all except for a small select few.
Some of the best characters to appear on screen. If you like crime dramas, SCI & detective stuff, you will absolutely adore this show. It's a must watch in general.