To really get the full experience from The Defenders, you would want to go into it having watched the first 2 seasons of Daredevil, as well as the first seasons of Jessica Jones, Luke Cage, and Iron Fist which are all available on Netflix.
The good news is you can still enjoy the story of The Defenders if you’ve never watched any other Marvel shows. It is an intriguing story that takes the strength and personalities of four very individualistic superheroes that have to join together in order to prevent New York City from being destroyed. The feeling of the show is interesting with the divergent personalities of the four heroes and even how in the beginning of the show each main characters scenes are colored specifically for them, really changing the feeling of the various scenes depending on what character you are watching.
One thing that is great about this show is that the heroes have such personal and relatable challenges that they feel a lot more human than the other superheroes in the Marvel universe like Iron Man or Captain America that are more like mythical figures.
I really enjoyed them pulling all the characters together for this team up and really hope they are working on The Defenders 2.