The first 2 seasons are great, season three has great moments but doesn't live up to the first 2, season 4 has some of the highest highs, but most of the B-plots are crap, Season 5 is probably around the same quality as 3 but without any super memorable moments. Season 6 sucks ass and sorta feels like a different show in the way it is structured. Season 7 starts kind of strong but severely drops off. Season 8 just makes you wish for some form of finality. Season 9 is pretty strong, and probably on season 3 & 5 level but still disappoints.

The biggest problem with Dexter is its big viewing numbers, a victim of it's own success. Showtime couldn't bare to get rid of it and swapping showrunners and writers constantly meant every season either ended being wrapped up in a nice bow or the loose end were wrapped up immediately in the following season. It just never feels like the story is heading anywhere. That said, it is an entertaining show, i'd say watch it until it gets tedious, like I said it tends to wrap itself up quite well most of the time.

Yeah totally the first 4 seasons are pretty good. John Lithgow in season 4 is great. I love me some doakes as well