Julie Andrews is a genuine delight, whether she's being fun or she's irritated. It's not just her voice, her whole presence is just delightful. George and Winifred Banks are excellent side characters, and the kids are as adorable as they need to be. Dick Van Dyke is a national treasure and I won't hear a word against him.
Structurally, there's not really a plot, but that makes sense given that it's based on a series of kind of episodic books. It's also very long. I think the length and episodic nature takes away from the character study of stuffy, cross Mr. Banks and how he learns from his children (and Mary Poppins and Bert) how to retain a sense of wonder and joy. But it's consistently fun. The music is delightful, the dancing is wonderful, and the adventures Mary Poppins and Bert and the kids go on are spectacular. I'm sure I have nostalgia for it but I think this stands up, to be honest.
The dings on the grade are for occasional bad costumes, bad makeup, the length, the imperialist nonsense. I'm honestly tempted to raise it back up because of the flawless animation/live action melding.