Underrated can also be described as personal favorites to me.  My number one would probably be Louis Friedlander's The Raven.  That's the 1935 one with Bela Lugosi for those who care.  As far as Tarkovsky goes his a brilliant genius who has gotten a surprising amount of recognition, certainly more than Parajanov or Yimou.
Well if I picked another nine for my list they would be as follows.
1. Les Carrabiniers (Godard) 
2. Faust (Murnau)
3. Mississippi Mermaid (Truffaut)
4. Kanal (Wajda)
5. Interiors (Allen)
6. Deconstructing Harry (Allen)
7. The Magician (Bergman)
8. The Long Goodbye (Altman)
9. Twin Peaks; Fire Walk With Me (Lynch)
10. (as mentioned before) The Raven (Friedlander)