I've made it about 5 episodes in. I had not watched Iron Fist before seeing The Defenders.
The problem with the show is that the choreography is really lopsided, and two of the four Defenders are damn near unlikable. Iron Fist is a whiny bastard who's actor clearly has no chops when it comes to being able to do fight choreography. Jessica Jones is a one note bitch to the point of being boring, who also isn't good at looking like she can actually fight. Luke Cage is more interesting, and he can brute force his way through fights, but he's woefully underutilized, and the ways the writers find to neutralize him are contrived within the context of the show.
Then there's Matt Murdoch, who's actor is the only one that seems to have fighting skills, but the camera doesn't stay still long enough to show it well. His actions and dialog aren't as good as they were in DD season one, but like Luke, he's still interesting.
In the end, it's hard to keep going. Half of the good guys are just bleh, the organization that they are fighting should have been able to wipe the floor with the Defenders, but they suck now, for some reason. The NYPD are the most inept, bumbling idiots in all of law enforcement, and it makes me irritated EVERY time they are on camera. And don't get me started on the damn Black Sky arc. Yawn.
