Magnum Opus: Don Bluth said that NIMH was the one project he most enjoyed working on out of all the films he made.
No Budget: The film was made on 7 million dollars, which is far smaller than the budgets Disney movies were accustomed to having, and some of that budget was achieved by having Bluth and some higher ups mortgage their houses. But because of the staffs resourcefulness and dedication, the films presentation and art doesn't give the slightest trace of it being a shoestring effort.
The Other Darrin: Almost everybody from the first film that reappears in the sequel has new voice actors. Jeremy and Mr. Ages are the only characters from the first film that retain their original voice actors.
What Could Have Been: MGM actually asked Don Bluth Studios to work on the sequel, but due to heavy development on Anastasia, it had to be turned down (Bluth had actually spoke of early story ideas in which Timmy and Martin would play hero and villain, albeit in reversed roles from the final product).
One wonders what would have happened if, rather than the travesty they actually made, the creators of the sequel movie had actually adapted Racso and the Rats of NIMH. While the book had its problems (Retcon, including elements from the movie which contradicted the original book, some Gary Stu-ism regarding Timothy), in most respects it was a very satisfying and exciting book which showed how the rats of NIMH really would (and should) have designed Thorn Valley. It even handled the "Timothy is the hero who will save Thorn Valley" plot far better than the terrible sequel did—complete with a great deal of Not Now, Kiddo and How Do I Shot Web? before the rats actually listen to him and Racso and he come up with ideas that actually work.