Yes, there's a difference between underrated and neglected by/unknown to the public. Almost all foreign language masterpieces fall into the latter category. Tarkovsky and Mizoguchi, among many others, are still awaiting proper recognition.

Some films i particularly like which deserve greater praise;
Maborosi, Alice in the Cities, Abraham Valley, The Green Ray, The Age of Innocence, El Cid, Tales of the Taira Clan, Pakeezah, Eternity and a Day (Cannes Palme d'Or notwithstanding). 

Then there are films admired by critics but which should be much better known; Sansho the Bailiff, Sunrise, 
Andrei Rublev, Mirror, The Colour of Pomegranates, Letter from an Unknown Woman, Celine and Julie go Boating, Ugetsu, L'Atalante, Orphee, Man with a Movie Camera, Spirit of the Beehive, even Tokyo Story and The Passion of Joan of Arc.

In America and the English-speaking world (and the top 100 here!), Kurosawa, Bergman, Fellini, Bunuel and some films by Renoir, De Sica, Eisenstein have had recognition, but far too many wonderful films and talents are terribly neglected. 
