In terms of Disney's animated features from the 80s, you can't really top The Great Mouse Detective. (Well, except Little Mermaid, which is technically an 89 release. I think of it as a 90s film.)
Great Mouse Detective was better than Little Mermaid. There, I said it.
I enjoyed The Black Cauldron, though. Though, really, the most unappreciated Disney film will always remain Treasure Planet.
but I also remembered that it was a bit scary to me as a kid 
