This show is definitely one to watch. Although some parts may seem cliche for a cop or detective show, it is solid entertainment with good all around morals.
I marked this as 14 and up mostly for the violence in it. There is a lot of gunfire in each episode, and the majority of the episodes revolve around crimes including murders, drug busts, kidnappings, etc. Of course, those are all things to be found in any other cop show on television today, so that's no different. Occasionally, dead bodies are shown and sometimes look gross or depending on the person, could cause someone to feel queasy. But those are a mere 10-30 seconds of a 40 minute show, so it can simply mean a turning away of the head if it's not something you want to see.
Others have marked sex as something in the show. Personally, I think this show has very minimal sex references in it, especially compared to the culture and what is seen on television. The show definitely doesn't revolve around sex and it's rarely seen. There were one or two episodes where sexual references were implied, etc, but nothing to be alarmed about or give a reason to not watch the show.
The cops in this show are great role models for kids to look up to. It shows the work put in by a former Navy Seal, Steve McGarrett, the main character in the show. His courage, bravery, and passion for taking care of the people of Hawaii rings true in every episode. There are constant references of looking out for family and protecting not only those you love, but those in the community and those in the country.
I would definitely recommend this show.