Sidney Lumet made some of the very best films of the 70s; 'Serpico', 'Dog Day Afternoon' and 'Network' being his best known. He also made some phenomenal British movies, the best of which are 'The Offence' (1972) and 'Equus' (1977).
I came to this film knowing very little about it, and am very glad for that fact, as it is not something to which justice can be done in a small summary of its story, nor is it a story that would make most people subsequently want to see the film. For this reason I will simply tell you that this film's power is not in its story, but in its exceptional delivery.
Lumet's films almost always have a certain unspoken quality to them that is very hard to define. I used to think it was the absence of a director's mark, but that is precisely the mark of Lumet; we don't know he's there. There is never any notion of self-consciousness in his films and, in a film this prone to pretension, that is quite a feat.
Shaffer's writing is inspired and meticulously researched, but never at the expense of the audience's attention. The psychology and philosophy that form the undercurrent of this movie demand that it be a slow paced film and that the viewer be prepared to ask themselves a lot of difficult questions, but the result is ultimately all the more rewarding.
I cannot imagine that the two leads could've been better cast. The criminally underrated Peter Firth manages to evoke fear, confusion and pity without ever resorting to acting by numbers. There is a coherence to his character which makes us want to put the pieces together, which is precisely why Burton's doctor is so drawn to him in the film. Burton is also on fine form, and Lumet does a wonderful job of keeping him on the screen despite the theatricality of the character and his dialogue, not to mention that of Burton as an actor.
This is not a film I would recommend to many people, as it is not easy viewing and it demands a good deal of emotional intelligence and the patience to use it. This is far from popcorn. If that statement makes you want to see the film even more, I recommend you do so as soon as possible.