Main problem with this movie: It's too long
I think Disney was really ambitious for doing this movie. I've read books about the making of this movie and how the animators all consider it a great achievement. It was an attempt to do something more 'high-brow' than what Disney was known for, and that's not necessarily bad.
I like classical music and I like animation so I really like the concept of this movie.
But I think the biggest miscalculation Disney made was the length of the movie.
I know some of the best classical music pieces can be longer than 30 minutes. They made cuts to the Rites of Spring so that it is closer to 20 minutes but it still feels too long.
Walt was always telling his brother they needed to do more work on these movies while his brother warned him about the costs. I'm sure that after Snow White paid off he felt more empowered to follow his creative instincts. Expanding a Mickey Mouse short (the Sorcerer's Apprentice) into a concert feature was a bold idea and I'm glad the movie was made.
It's just that I think popular audiences weren't ready for a 2 hour cartoon like this. And as a modern viewer, I actually find it fatiguing too even though all the segments on their own are worth watching.