First off I will say that I am really enjoying this season, but for me it's turning out to be the weakest of the 5 seasons. Season 3 was mostly a disappointment because of the final episode, but Jimmy Smits Miguel Prado was a great character and it was a pretty exciting story. Season one was all about getting to know Dexter, and The Ice Truck Killer story was amazing. Season 2 had The Bay Harbour Butcher story and had Dokes, Lila, and Lundy as adversaries (all great characters) And of course Season 4 had John Lithgow as Trinity which made it the best season of the lot for me.
Season 5 is lacking when it comes to Storyline compared to all the other seasons and also a great adversary for Dexter, Quinn just does not cut it for me. Maybe Peter Weller's bent copper character might change things, but he only has 7 episodes to make an impact.