I thought it was great! It lived up to my expectations, but in ways that I wasn't expecting it to, if that makes sense. Overall, the film's strongest asset is its atmosphere of paranoia. By the end of the movie you don't know what to believe, who to believe, or why to believe it. I thought it had a brilliant use of color (or lack thereof, I guess a more brilliant use of color splashes), music and sound, actually the whole look of the film is great. It does a fantastic job of playing with dreams, flashbacks, and hallucinations that make the whole thing seem like some sort of bizarre nightmare. And while you could probably figure out the ending well before it happens, how they get to the result is still very intriguing.
In terms of the Scorsese factor, in terms of comparing this to the rest of his work, this isn't one of his greatest. But that's because you're comparing it with some of the best films ever made. That being said, Scorsese is probably what saved it. I could easily see this same film being RUINED by a lesser filmmaker. It was Scorsese's veteran restraint that made this good. An inexperienced director likely would have shown too much craziness, and too early. There was almost a Jaws-like patience for showing some of the things being built up in this movie.
So if you haven't seen any movies yet this year, check this one out, I think it's the first great movie of 2010. After letting it sink in for a couple of days, I'm still thinking about it, which is a good sign of greatness to me. If I have time, I'll definitely check it out in theaters a second time.