Just finished the first season, on the tails of watching DD.
It looks like they are going to try and be true to the emotional roots of how these series are going to be presented. DD was the safest, as he is the most 'classic' superhero in terms of tone. Clear place to start, with a lot of room to grow into the more philosophical ninja/Stick/Mephisto territory and building upon the law room angle. JJ is pure noir. I would like to see it go even deeper, into more of a realm of mystery. Cage will be fun, 70s grit with an edge of blaxsploitation. Iron Fist will bring more of the 'Marvel' element that people have come to enjoy in the movies, closest in spirit to Thor, I understand why that introduction will be last.
Remember that this is an introduction to these characters, these first seasons. One thing that they are doing right is giving each character a Ying to their Yang, so to speak. The villians are at least as compelling as the heroes.
As for JJ issues with her powers being inconsistent....
Other than Cage/JJ (understandable), I really like the subtle intertwining of the different franchises. The appearance of Nurse Temple and Mistress Gao. They don't hit you over the head with crossover possibilities.
When it's all said and done, Defenders could be top five in the superhero genre. So much potential.