I agree with everybody else who says this show is addictive. It has some unknown element that draws you in and makes you want to keep watching.
The characters, despite their many flaws, are all likable. The acting is good, there's a lot of funny lines, and in some scenes, strong family values are shown.
That being said, there is a lot of sex. But, for teenagers, sex is everywhere, so the show isn't really doing anymore harm than real life does.
Language is strong, sometimes, but nothing that a TV-14 rating doesn't cover.
There is violence, about 65% of the time. Drugs and alcohol are almost always present, even if they are just an understated part of the scene.
I love this show. My 13-year-old sister and I watch it together, and I wouldn't want her to watch it by herself or with her friends, or with our parents, for that matter. I think it's a good show to watch with young teens, so if they have questions or want to talk about any of it, there's someone there for them.
However, my sister is very mature for her age, and I wouldn't recommend this show for kids under the age of 14, and they should watch it with a parent or an older sibling.