This was not that great. So far, only Daredevil has been consistently really good out of these Netflix/Marvel series, though I am still holding out hope for Jon Bernthal as The Punisher as he seemed like a perfect casting choice and was great in the Daredevil episodes he was in, and if his series' writing quality is at the same level, it should be decent.
In descending order of quality, i would go:
1.] Daredevil - great cast, great writing, nice complex well-paced story layout
2.] Luke Cage - ok cast, ok to mediocre writing, ok to slow predictable story layout
3.] Iron Fist - ok to limp soap opera-level cast, mediocre writing, mediocre story development
4.] Jessica Jones - meh, meh, and more meh. Krysten Ritter was annoying in Breaking Bad but that was ok because her character was supposed to be an unlikable Yoko-type climber. She plays Jessica Jones almost the same, with maybe a few more slouches and smirks, probably because that's the extent of her range, but the problem is that JJ is a way more interesting character than she seems capable of giving life to. She's promoted as a sex symbol and she does have a nice ass, but that's not really enough to carry a series. David Tenant was ok, but featured more like an expensive added ingredient than an integral part of the whole. Not that any of that would have mattered as much if the writing had been a little better, well, much better.
The biggest problem with The Defenders was that these were the components it was put together from, and they were uneven in quality at best. The Daredevil elements were ok, but diluted by the whole, and the rest were kind of just weak versions of their already weak selves.