My kids (12 and 13 yo) and I are watching this on netflix this summer. We are finished with three seasons and we all love it. There are some things though that parents may want to know before they get invested in the show. It is addictive!
The violence is choreographed so that is not an issue for me (and I really hate violent shows and games). It is no worse than fight scenes in other crime procedurals. It is not bloody. The use of guns is debated regularly on the show. The main character refuses to use them, and the message here is a good one - when someone dies it is serious and it changes you. For a generation that plays Call of Duty etc. this is important to hear.
I find the show though to be fairly sexual, sometimes uncomfortably so for me. There are scenes of casual hook ups (no nudity, but there is undressing); using sex to solicit information; a good deal of talk about sex; some stalking references. Now this is a comedy, so these things are funny and light hearted. They are also ironic or unrealistic. But they are there.
The relationships also do not become marital relationships until season 2. Couples live together - they are very committed and actually good role models for positive relationships - but if you are trying to teach your kids to wait before marriage this may offer some counter messages. I just simply used it to talk to my kids about our values and how they are different and similar to those in the show.
The second season in particular also presents women as sexual objects. They have little to contribute in terms of dialogue nor are their characters really developed at all. They are show from the perspective of the men in the show. Fantasy scenes include women with wind swept hair, little clothing, etc. Again they are funny... but I talked with my kids about this - that women are more than just something to look at or to be pretty for the sake of guys. This concerns me for the message it sends my son. My daughter and I have talked about what "girls" are enough that she knows it is not real world. I have become more aware though of how much harder this message is for boys to understand. Season three gets better on this issue. But for the a good part of the show, even the fight scenes with the female characters are meant for men to watch (fighting with skimpy outfits on etc.). Clearly someone was working out his fantasies here.
All of that said, we do love the show. The characters are great and endearing. Things like trust and friendship are regularly talked about. The importance of family is a strong message throughout. It is fine for most families. Other parents may want to pause.