I'll tell you what is underrated, and that the incredibles. It's the only superhero film that has had a breath of realism in it with a real family connection shining through
just the idea of a retired hero wanting to relive the good ol glory days is a really humanising concept.
nothing else comes to mind...
The Incredibles certainly isn't underrated. When it was released, it made several movie critics top 10 lists for 2004, nominated for 4 Oscars, won 2, won a Hugo Award, and a Saturn award, just to name a few awards it won. When it was released on DVD in 2005, it was the highest selling DVD for the year.
For real under-rated animated films, The Iron Giant and Titan AE definitely come to my mind.