So looks like "Shutter Island" is a must see after all. The reviews are rather mixed and conflicting: just compare the piece by the NYTimes and a rather flattering one by Roger Ebert here.
Myself I've always found Scorsese and DiCaprio collaborations worthwile if not more. In fact, I wasn't so crazy about "The Departed," but both "The Aviator" and "Gangs of New York" proved to be quality entertainment. I also often found myself defending DiCaprio whenever someone suggested that he "couldn't act." I was never a big fan of his, but I know for a fact that he's a good actor and his film career is not defined by starring in "Titanic."
While $40 million collected by "Shutter Island" in first opening weekend doesn't guarantee it's a great movie, I have a gut feeling (based on all I've read and heard) it will be worth my time. And when it comes to films, my gut feeling is usually right.