I'm eight episodes in and finding it is not as bad as many of the reviews let on. It is definitely the weakest of the series, so far, in my opinion (and Iron Fist was my favorite of the four comics-wise). It suffers from a lack of compelling villain up to episode eight, no Kingpin/Cottonmouth/Purple Man quality acting/writing for the nominal villains so far (Madame Gao, various Meachums).
I'm enjoying Jessica Henwick's Colleen Wing a lot, and Rosario Dawson steals every scene she's in (as does Carrie Anne Moss).
Can definitely see the pieces moving into place for the Defenders. Should be interesting.