Nothing - repeat absolutely nothing - in this film is sub-par. The acting, especially the inhuman physical contortions of Nikolai Cherkasov as the Tsar himself, is uniformly excellent. As is to be expected from Eisenstein, the direction is perfect. Eisenstein's compositions create painterly tableaux that can be watched endlessly on pause (especially now that Criterion has issued both Ivans on DVD), allowing the audience to take in the full breadth of this man's genius. Additionally, unlike, for example, Alexander Nevsky or Strike, Ivan the Terrible Part II (and part I) benefits from a smoother pace and better editing, putting Eisenstein's theory of montage to its best use since Potemkin.
For me, however, what two key components of this film set it apart from its prequel and Eisenstein's earlier Potemkin and October.
Those components, as you can imagine, are its more pronounce political allegory and its color sequence towards the end.
Certainly October and Potemkin were highly politicized affairs, both celebrating the Communist victory in Russia. In Ivan the Terrible Part II (and to a lesser extent Part I), the audience bears witness to a moment of challenge wherein Eisenstein becomes critical of the course his country and its post-Lenin leaders have taken. As such, Ivan the Terrible becomes one of the bravest moments in film history and, for that alone, should be commended.
Brilliant as a political critique, the film also represents a dazzling demonstration of how color could be used in cinema. The colorized dance at the end of the film rivals and prefigures the technicolor explosion in Douglas Sirk's 1950s melodramas; furthermore, it reveals that color can be used to achieve specific effects. It does not have to mimic reality; rather it can be used artistically to enhance the mood and atmosphere of the film.
Taken as a whole, the two-part Ivan the Terrible is a masterpiece of Russian Cinema and should be required viewing for anyone with the slightest bit of interest in film. My preference lies with the second part, but both are fantastic moments in film history.