Visually a classic, but weaker story-wise than other Disney masterpieces
The film has three great strengths.
First, the animation, which is some of Disney's finest. Thankfully it was made back during the era of Disney's greatest quality (not the later "scratchy" animation from Dalmatians onwards), so it's stunning to look at. The colors, the shapes, the sheer imagination. Breathtaking.
Second, Alice herself is extremely endearing. Her design is adorable, with her fair hair, big blue eyes, and pretty girlish outfit, bloomers and all. Her character is simply delightful, with her manners and etiquette on the one hand, and her imagination on the other.
Third, the moral is a very good one: that while one may wish at times for chaos rather than "boring" order, in fact chaos or nonsense quickly becomes more boring than the order we resented, and ennui and frustration develop.
This has two particularly relevant real-world applications:
On the one hand, it demonstrates that in how a society governs itself, order and stability are far better than either anarchy or petty despotism.
And on the other hand, in the world of art, it shows what happens when traditional ideals of form and beauty are sacrificed for juvenile abstraction and primitivism. Our art world today (painting, architecture, etc.) is still an Alice-in-Wonderland world of meaningless chaos, which has indeed grown boring through formlessness.
The most effective scene, by far, in the entire film is the one in which Alice breaks down in tears and finally realizes that she's had enough of the nonsense she wished for, and that she wishes that she could go home. Suddenly, the story becomes very moving, because you see before you a scared, lost little girl, and your heart goes out to her.
The trouble is, the same factor that is the film's strength of theme is its weakness in story: to create this tedium-of-nonsense perception, the film actually has to have the audience feel the same frustration at what they're experiencing as Alice does. Thus, we end up just as impatient with the film as Alice is with Wonderland itself.
The film is just too episodic. It needs to be, of course, because that's its theme. But the result is still a viewing experience that gets tiresome, no matter how much we adore Alice (and we do), and no matter how creative are the visuals.
Definitely a classic, but weakened by the necessity of its own moral, which required an episodic structure.