The trick of the film is to have the audience accept that Mozart killed himself, by indulging to the powers of writing a requiem. And it manages to do that - although it felt a bit long at one of two points, until that important revelation and connection between Mozart's inner working and his physical condition is established. The most intriguing thought for me was how Salieri arrives at the conclusion that not he himself kill Mozart, but he managed to cheat god into killing him. And his madness depends about the upholding of this mental construct.
There are many other aspects of the films which fascinated me: the scene where Mozart dictates the composition is quite amazing, also from a musical point of view. That little deconstruction and analysis of that little part of the requiem reminded me that there are few things as gratifying as studying the masters - independent of their craft.
Some of the shots were amazing. Especially seeing Mozart direct throughout the various stages of his career for filled, empty, bored and excited audiences was interesting. The face of the evil Salieri, halfway buried in shadows and the amazing physiognomy of the emperor were all great visual treatments of the time. I was particularly amused by the treatment of the subject cleavage by Forman.