I'll agree Ericsson has improved, but I don't think he is a top two D man! He still turns the puck over too frequently, generally doesn't think the game all that well, and doesn't use his big body effectively in most situations. And when you think about it, this is his sixth season playing with the big club! I expect more from him for the salary he is paid and for the years of experience he has! He has developed too slowly, and in my opinion, the Wings should look at trading him while they still might get something for him, rather than letting him walk as a free agent!
His first full season was 09/10 prior to that he played 8 games in 07/08 and 19 games in 08/09. He was drafted 291st the last player drafted in '02 which was the year he switched from center position to defense.
I'd say he has done quite well.