Fascinating, imperfect and sad. I want to say that Cherkasov was "born to play this role", but it seems like he was born to play Alexander Nevsky and Ivan the terrible as well. Perhaps you can look at it as a kind of (very soviet?) trajectory - the ideal hero descends into madness... It's unfortunate that the script isn't tighter / sancho isn't better.
Of course, adapting a monumental classic to the big screen can only be an invitation to read the novel and never a substitute to the experience. I admired Kozintsev's evocative, lyrical eye for landscapes as well as the entire cast and crew's affection for the story. There are scenes of awesome power, such as the climactic windmill scene, but my favorite remains Don Quixote's tender dialogue with the lion.
Like many Soviet films, gorgeous compositional sense and intelligent camera movement, but lousy colour process. Moskvin and Cherkassov's input reminds me strongly of Eisenstein's "Ivan The Terrible"; Cherkassov (a double for Gunnar Bjornstrand) seems like a gangling, gawky spectator at his own pageant -as if Ivan was freed from his own delirium, cleansed of his evil, again finding nobility in virtuous adventures.