I wish there was just one movie which wasn't Japanese and which would break the mold. Something with depth and maturity; without any talking animals whatsoever, completely devoid of anything remotely cute, but not slipping into some caricature-like style either…
I could spend several pages listing off animations that fit that description, and that would just be off the top of my head. I shall however settle on saying that if you believe there to be no eastern animated films that are unique or ground-breaking, you are simply not looking beyond the very surface of eastern animation.
In any case.
As far as underrated goes, I really enjoyed 'When the Wind Blows'. It's from the 80's, and I've never heard anyone discuss it off of the internet. And I know it's not exactly underrated (I've heard it discussed), but ‘The Yellow Submarine’ was one of my favorite movies growing up. I only mention it because many of the people I run into have never heard of it (;_;)
In a similar, trippy, vein, ‘Paprika’ is good. But virtually unheard of amongst some groups.