I've read some reviews on this soundtrack and what every times surprises me is that pretty much no one is aware of that this ost is actually a collage of motifs from classical stuff:

Adventure theme = Schumann's 3rd Rhenish symphony
Four-note danger theme = Rachmaninov's Symphony No. 1
Three-note choral motif = Janacek's Glagolitic Mass
Other choral motif = Bartok's Cantata Profana
Willow's theme = Mir Stanke Le
Bavmorda's theme = Prokofiev's October Revolution Cantata

...plus excerpts from Mozart's Requiem, Grieg's Peer Gynt, Prokofiev's Alexander Nevsky and Smetana's Moldau