My wife and I absolutely loved this show. Just watch it if you enjoy very dark, suspenseful stuff with good characters and almost a casual light attitude even though the whole thing is so dark and gory. I just need to warn you, stop watching after season 5. I loved season 5 but after that my wife and I were devastated by the last seasons. We think it went down the wrong path and ruined the show for us. Go through season 5 and then just read the endings of the next seasons on some blog or something and forget about watching it. This will make your memories of the show stay great. Trust me, don't watch those final seasons.
One of my favorite TV series of all-time, possibly one of the best ever made for a time. The acting, writing, and plot are all so well-done and unique. The only problem is the unreasonable expectations from the first seasons make people hyper-critical of the latter ones. In my opinion, the only "bad" season was 8, and a lot of that has to do with the manner in which the writers end the story (no real finality). If you have yet to watch Dexter, I envy you as I wish I could go back 15 years and watch the first episodes again. I can't recommend this show enough, it's the series that made me love television.