The biggest challenge to Downey's entire performance as Chaplin is possibly his imitations of Chaplin's film moments as well as his vaudevillian acts. Downey is quite effective in doing both of these. He is firstly a intensely believable as a vaudevillian, and certianly has the spot on timing and ability. In his later portrayal of Chaplin's film sequences he is again completely believable, and accurate to the manner of the real Chaplin.
Downey is particularly effective in this aspect of Chaplin, because he never really makes it seem that he being overly technically, nor does it feel like an imitation of Chaplin. It instead feels like the actual manner of Chaplin, and he does indeed a very strong job of being able to have the perfect feeling of all the Chaplin footage, from his early silent routines, as well as his recitation of the final speech of the Great Dictator.
Downey portrayal of Chaplin as a man, is not an extremely complicated one, but it is an appropriate one. Chaplin does not really undergo any major changes throughout the film, and always stands as an entertainer, and as a man who believes in his message as well. The one major vice the film presents is his involvement women.
The film shows his various relationships, but at the same time does not delve overly deep in many of them implying most of them are purely for physical satisfaction, which Downey certainly presents in a realistic fashion, showing that with every relationship Chaplin is always more concerned with himself than other, without overplaying it, suggesting it just as the nature of Chaplin.
Other than his relationship Chaplin is portrayed as basically a nice enough man, and Downey gives the part the proper charm. His most major transformation as Chaplin though is that of his aging, as well as just his adjustment into his wealthier position. Downey actually handles both of these aspects quite well, and his development of his accent from working class in the beginning to wealthy ends is very well handled by Downey.
His other transformation is his aging which certainly has a lot to do with his makeup which becomes quite heavy near the end of the film. Downey though does not let it do all of the work for him though, and believably wears the make up, and shows his aging in more subtle aging in his voice and physical movements.
Otherwise than that there is not much more to say about his performance, otherwise that it is charming, and believable. This another performance though that I still think could have been given a little more by the film itself. Due to the almost perfect presentation of Chaplin, Downey can only go so far with the role, which is so far that it most certainly is a good performance, but not a great performance.
