DiCaprio has never been immature; he has always been a talent. Here, however, he delivers his worst performance ever; I absolutely agree. One expression (one) from the beginning to the end of the film: whether they kill his father or he sleeps with Cameron Diaz, it's the same for him. Maybe they told him he was on the set of Terminator...
As for the film, I don't know, I only saw it in the cinema at the time of release; I remember enjoying it and that by the end I had a sore ass. But all in all, Scorsese has been "finished" for a while; his "food cinema" (made for eating, to fill time, or whatever you want) remains an aesthetic and wonderful cinema, but in this wonder of direction and photography, he often gets trapped. There isn't a character in The Departed that takes flight, none in Wolf of Wall Street, and in Gangs of New York, the character of Daniel Day-Lewis owes more to D’s performance than to M's undeniable charisma. In The Aviator, it's a different story; we start from characters that are already legends and have charisma from the screenplay, but they are then managed poorly from start to finish. The Aviator is a film made for those who don’t know the characters involved, but know all the cinema of the '40s, which seems like a rather elitist premise for a film from the 2000s produced by Hollywood and costing one hundred and ten million dollars.
Then, to be fair, with what he has done in the past, he is free to do whatever he wants, but it cannot be denied that the cinema he offered until the first half of the '80s had a decidedly higher artistic value. Even Casino, which I really like, compared to Raging Bull or even just to Goodfellas, has an alarming emotional sterility.
Then again, what Scorsese did before the '80s was something else entirely; he was writing history. And, all in all, nowadays he can do whatever the hell he wants until he decides to make a fool of himself.
Ah, then there’s Shutter Island… no, come on, let’s pretend Shutter Island doesn’t exist.