This show is absolutely amazing! It is incredibly refreshing after all the new Marvel content. Unlike their new shows, this series has character development, the characters are likeable, there are many twists and turns, and they're not afraid to kill off characters.
About the characters: Even when they add on new characters, they are likable. They aren't this, "Hey, I'm new and I'm gonna take away a lot of screen time. And don't forget... You're gonna hate me." Instead it's, "Hey, I'm new. You're gonna grow to like me a lot." Also, the characters get developed, they're not invincible, and they have struggles to work through.
About the story: This series has such amazing stories. I'm onto Season 4 and every season has been better than the last. Along with this, the series has so many twists and turns and, like I said earlier, they're not afraid to kill of characters. It seems as if, so often, writers now a days leave characters alive, when they should have died, because they are too afraid to write in new characters. But this show avoids that move. Also there is so much emotion, but it doesn't turn this series into a soap opera, by any stretch. Along the lines of Soap Opera, this series doesn't have forced dialogue. (Such as in Arrow or The Flash) The dialog seems smooth and real.
Parental Guidance: This amazing piece of cinema does have some content to be concerned about. There are a few sexual scenes in Season 1 and a few jokes. It is extremely easy to predict that the scenes are coming if you pay attention. After season 1, it gradually decreases in amount of sex content until season 4 when it shoots up again. There is one thing that I know many families don't want their kids to see. That is gay storylines. So, in this series everyone is straight (so far) except for one man who shows up in Season 3. They mention his boyfriend(s) twice. Season 1 has minimal violence. (Nothing like Daredevil or Iron Fist) Seasons 2, 3, and 4 get to be more violent. (Medium PG-13 I'd say) This series is rather peppy until Season 4 when it gets to a darker tone. (Mainly because of Ghost Rider) But the series still has a lot of humor and the two go well together. In the end, I believe it is fine for a 14 or 15 year old to watch.
I highly recommend this to anyone who likes action/spy/superhero content.