Saw this last night. Interesting film. If you've seen the trailers then you may be in for a suprise. Scorcese is pulling a bait and switch. You THINK it's about one thing but it's really about, well I don't think I'm spoiling anything here, it's about filmmaking. Literally. Complete with mini-lecture. So be warned, if you think it's just going to be kids running around solving a mystery amidst wonderment and stuff, er not so much. That said it's very well made, looks beautiful. Does it need 3D? Frankly, no. But then most 3D films lose nothing in 2D IMO, with the exception of anything done by James Cameron (see Titanic 3D thread).
There is also a distinct feeling of 'let's use this film to educate children by using SAT words and emphasizing the value of books'. I kid you not. You'll understand when you see it.
Sacha Baron Cohen steals the film (surprise) despite a slightly weird performance. Interesting character behavior, but the guy is so good he makes it work. Sir Ben is of course, phenomenal and will probably be nominated, especially given the significance of his character.
All in all a good film. A little slow. Just be prepared for less adventure and more Reading/Film Rainbow.