I loved the costuming. (Especially Mary's three marvellous, vividly-colored coats.) I loved the scenery. (The full house on stage, with a third story that lowers to the floor whenever there are scenes in the children's bedroom.) I loved the use of silhouette in group sequences. The rooftops dance sequence were well done. The singing was solid. I loved how tidy the plot was, with all small mentions of things having a payoff of some sort.
Things which were slightly less satisfying: No birds in the "Feed the Bird" sequence, when there were several other birds featured elsewhere in the musical. How slightly arbitrary the setting of "Supercalifragilisticexpialidocious" seemed, if entertaining. I was bothered that the son handed his father a telescope to examine it closer after he thought he'd seen a shooting star. (That's one slow shooting star.)
What I really loved more than anything else, however, was how perfect the evil nanny of Mr. Banks' childhood was. She was fabulous - strong, confident, good singer, good song and perfectly mundanely evil. I was only sorry her presence in the musical didn't last longer.