From a pure film making perspective, Shutter Island has everything: Great acting, cinematography, character development, storyline, twists, clues dropped throughout, etc. Scorsese is a master filmmaker and I greatly respect his work, Shutter Island is no different. Exceptionally thought out and executed. I am sure it will win several awards.
If I was making a recommendation to a friend, I would say skip all together. Its an emotional and psychological train wreak of a sad movie (sad as in actually sad, not poor quality), and it explores emotions, sadness and terror that I do not think will make you a better person. I think that sometimes there are attempts at subliminal programming as well as bold suggestions, and Shutter Island has both. I wouldn’t want my children to see it, simply because it takes you to places most humans should never visit. In some ways, I regret seeing it myself.