Well, Frozen is an example of the kind and quality of animation that's never entirely left Disney, even during the darker time periods of the animation studio -- and which, just to say, a lot of other studios would probably be happy to have their darker periods defined by some of the movies that define Disney's.
And on the specifics, Frozen shows how brands that do last for just about forever manage to do it. They go for that which is timeless, for things which will resonate decades after the advertising itself has ended.
Coca-Cola does this really well. Coke would like to teach the world to sing. The sentiment is timeless. The shirts are a little period, but the hairstylings even today aren't so of their day that you notice them. And Coke is The Real Thing. It's Always Coca-Cola. McDonalds has done this really well in many of their best advertisements.
And Frozen will be timeless without being frozen in time. It's about two sisters, with a classic family bond that anyone who's ever had a sibling or a best friend or pretty much known anyone who has will understand. It's about bad decisions, of running away from problems you need to face, or not being cognizant of the consequences of your action. About bad decisions when you rush into things.
The animation is as beautiful and timeless as the themes and basic underpinnings of the story. Really, really beautiful. Disney has been melding computer and hand-held animation as far back as the waltz sequence in Beauty and the Beast, and they do it really really well now. [as a complete aside, I thought watching the trailers before the film that Walking With Dinosaurs looked more real and live-action than Desolation of Smaug.]
The songs aren't quite up to the heights of some of the great movies like Little Mermaid and Beauty and the Beast from 15 or 20 years ago, but they are more than good enough.
The bones of the plot aren't quite perfect. Falling in love with Hans happens a little too quickly, a little too easily, that you can see the plot mechanics at work. I'm sure an 8-year-old isn't going to notice this, but the adults certainly won't be surprised very much when Hans turns out to be not such a good guy after all. I could have done without having the weasels come from Weaseldon.
But overall, if you want to know why we still have Disney movies after almost a century while no other animation department has been around for near as long, Frozen is a good example. It goes timeless.
The best Pixar movies do the same thing.
Which is why, if you go looking at the box office rankings for animated movies, you find lots of Disney and Pixar, and other than for the Shrek and Despicable Me movies not very much else. It's a little imperfect to compare box office against different eras, but for what it's worth, the highest-rated Dreamworks movie other than Shrek is the one that is inherently most timeless, which is How To Train Your Dragon.
It's no accident that the Despicable Me movies have a certain timelessness in their father/daughter dynamic.
The Shrek movies stand a little aside from everything else, and I think Dreamworks has been a little like the author who borrows from great writers without understanding what makes them great. In many ways the Shrek movies were of a time, melding animation ideas with the height of the Austin Powers thing. All too often since, Dreamworks has doubled down on thinking that fast-paced frenetic animation full of pop culture references is the way to keep replicating Shrek, and I don't think that's correct.
Even in its worst days, Disney could come up with a solid, reasonably timeless movie like Oliver & Company with songs that at their best I'd say are better than those in Frozen. And in fifty years, it wouldn't surprise me if more people are paying attention to Oliver & Company than to Madagascar.