Very clever film-making, so appropropriate to the biography of this fascinating man! It's worth watching just for the way it's put together, even if you aren't interested in the storyline. Rush is fantastic, his strongest performance to date I reckon.
Essentially this is a one-man show by Geoffrey Rush, with a little help from the supporting cast, many of whose characters Rush also plays some of the time. By the way, although the listing on this site mysteriously gives him top billing, fans of Stephen Fry will be disappointed to learn that he's in this two-hour film for about five minutes. Rush is superb, even managing the rare feat of convincingly looking older as the film progresses, though a lot of the credit for that should probably go to the makeup department. Just about the only things he can't do are Sellers' Goon Show voices (though at least he's better than the two actors in the thankfully very minor rôles of Spike Milligan and Harry Secombe).
The main problem is that Sellers is such a consistently unlikable character that, excellent though Rush's performance is, there's a coldness at the heart of the film which sometimes means that the viewer admires its technical virtuosity while not really being involved. According to many people who knew Sellers, this isn't an entirely unfair portrayal. However, it's probably an oversimplification to take Seller's own claim that there was no "real" Peter Sellers to be literally true just because it's his most famous quote, and a more complex and interesting film might have resulted if he'd been portrayed as more than a completely empty man who never stopped being dominated by his overbearing mother even after she was dead.
For instance, although it's touched upon in the scenes where he unquestioningly accepts the advice of the ludicrously fake "psychic" Maurice Woodruff (Stephen Fry), nothing is really made of Sellers' unbelievable gullibility about the supernatural, to the point where he walked off the set of "Casino Royale" because he honestly thought Peter Ustinov's amateur conjuring tricks were real magic, therefore he must be in league with the devil and might put a curse on him! This and other strange aspects of his character heavily imply that behind all those masks, the real Peter Sellers was fighting far nastier demons than he ever admitted.
Perhaps some more of that might have been interesting, rather than the deliberately artificial narrative techniques adopted here, where Rush as Sellers frequently breaks the fourth wall by talking directly to the camera and walking off the set, or suddenly switches character to someone previously played by another actor, all of which occasionally gets a bit too clever for its own good. But on the whole, it's a good if sometimes oversimplified portrayal of a talented man who played the clown for the whole world, while being at lot less fun to be around for those closest to him, especially himself. Just don't expect too many laughs.
Geoff had his work cut out......almost a Seller's job. Not very kind to Sellers, but perhaps they were using known material.