Don Bluth, former head of Disney animation in the 70's and early 80's, broke away from Disney to become the creator of his own original films. This includes animated classics from the 80's, such as The Secret of N.I.M.H, The Land Before Time, and An American Tail.
After Don left Disney in the 80's, Disney went through a period where the quality of their animation was subpar compared to Disney's pervious successes. For this reason, their movies were not as well received, while Bluth's films were on the rise. If we compare the storytelling and the animation of Bluth's movies during this period, with that of Disney's, we can clearly see why Disney was going through what some call their "dark age". It was the first time in the company's history that they had direct competition, and because of the brilliance of Don Bluth's work, they were losing. I believe his triumphs in the 80's, went on to reignited Disney's fire. If it weren't for this, Disney's The Little Mermaid may not have been made.
While he had a big high in the 80's, the 90's were tough for Bluth. The one exception to this was his film Anastasia. At this same time his former employer, Disney, had a renaissance with The Little Mermaid, Beauty and the Beast, and The lion king.
Bluth's last film came out in 2000, Titan A.E, but it unfortunately only made an good impression amongst strong followers. Bluth has not made a new film since, however this is about to change. In 2015 he launched an IndieGoGo to make his new film based on the very popular video game he created, Dragons lair. Not only will this be a labor of love from Bluth, who is now age 79, but more importantly the animation will be hand drawn just like the golden age of animation he helped to create.
If you liked The Secret of NIMH, here are some foreign film recommendations that have the same spirit of Don Bluth's earlier films, and the beauty of 2d animation.