Just came back from seeing it, and I LOVED it! Mary Poppins is my favorite Disney film and one of my favorite films in general, so this movie had some big shoes to fill. Naturally, nothing is going to quite live up to the first film (which is Practically Perfect in Every Way), but I thought this film did an excellent job of bringing the spirit of the first back. I haven't read PL Travers' books, so I'm not sure if this one's story aligns with any of the books, but I liked it very much. It worked very well. It was obvious that they tried to parallel the first movie (hopping into the bowl = hopping into chalk paintings, Visit with Cousin Topsy = Visit with Uncle Albert, the Lamplighters ("leeries") = the Chimney Sweeps, the balloons at the end = the kite flying of the first, and so on). I thought it was well done. The songs weren't quite as catchy, but they're new to me whereas I've been listening to the others since I was born.
I went with my parents, who are in their 70's, and they both loved it too. My dad is a musician and lover of all things musical, and he enjoyed it. As soon as the credits rolled at the end he said he thought it was wonderful. He admitted later that he really wasn't expecting much, as he held the first movie in such high regard, but he was very pleasantly surprised.
The cast was superb, in my opinion. Emily Blunt did a fine job as Mary, and I enjoyed her haughtiness. It cracks me up how she's always "just so" and usually primping on her hair and perfectly poised while "stuff and nonsense" is swirling around her. I really thought Ben Whishaw's performance was phenomenal. He's such a gifted actor. He broke my heart. Everyone else was wonderful too, especially the guest appearances. I knew about the first guest appearance in the bank, but was unaware of the second and was delighted. I feel that role was probably meant for a different actress *ahem*, but I assume she declined and this one was a very worthy person to take her place.
The last thing I'll say is that I hope the people who go see it don't read negative reviews ahead of time. It's interesting to me that a movie that is supposed to be about finding the magic and wonder of childhood once again is torn to shreds by cynical adults who seem unable to get over themselves enough to just go in and enjoy the thing for what it is. I was 10 years old again sitting there in the theater today, especially during the part where they go into the bowl. My 76-year old mom and I literally danced our way out of the theater to the music playing during the credits.
ETA: I just saw what I feel is a very deft description of the film: It's like a love letter to the first movie.
I think that's a perfect way to look at it.