Series one is probably the weakest as they were finding their feet. Edmund was a sniveling wretch in that one, but everything after that he was a true bastard. Still cowardly, but in a much cooler way.
Series 2 is the best by a long shot, and essential viewing.
I wasnt overly impressed with series 3 initially, but it has certainly grown on me over time to the point that I really like it. I think its cause it just had so much to live up to following the classic that was series 2.
Series 4 was great. While still not as good as series 2, it was certainly a lot more instant than series 3.
The two one offs (Back and forth and Christmas carol are ok, but not essential viewing.
