Warning, here there be spoilers.
Wodehouse is notoriously difficult to film. The usual reason given for this is that Wodehouse is a literary writer and half the fun is his wordplay. But Wodehouse wrote Byzantine plots that do not translate well to a medium where simplicity is the key to understanding.
Take impostors, for instance. Wodehouse loved what we today would call Identity Theft. He had characters staying in other people's houses under false identities all the time. The plot of "Picadilly Jim" is so involved and convoluted one character is staying in another person's home disguised as himself, and he begs a man who knows him not to reveal his true identity.
On top of all this, Wodehouse's fans know his books too well for short-cut liberties to be taken blithely. When one films Wodehouse, one takes one's life in one's hands, as in an aerialist act performed without a net.
This production started well by choosing a little-known Wodehouse novel, written before his "Golden Age" classics. The Jeeves and Blandings Castle sagas were only just poking their little heads out of their shells when PICADILLY JIM (the novel) was written.
It's a little known book, and not a very important one in the Wodehouse oeuvre. And they give it to you fast and slick. Like the "Airplane" movies, if you don't laugh at one thing, they keep throwing Wodehouse at you until they tickle your funny bone somewhere.
For Wodehouse purists, the adaptation sticks close to the books. Where the script deviates from Wodehouse writ, most of it is justifiable and a lot of new material is funny. And why not? It was scripted by Julian Fellowes, who, as an actor, played many a character that might have tumbled right out of Wodehouse.
Sam Rockwell ("The Hitchhiker's Guide to the Galaxy", "Midsummer Night's Dream"), tackling the part of the eponymous Jim, is one of those actors who seem born to play Wodehouse at some point. I'm glad he's playing a minor Wodehouse star.
The rest of the cast is fine, with Tom Wilkinson, another Wodehouse natural, as a standout. Geoffrey Palmer has a good turn as a Wodehouse butler. Frances O'Connor is a trifle too neurotic for a Wodehouse female (the younger Wodehouse women are usually more together than the men, though they become unhinged with age). Her neurosis is firmly grounded in the book; the script flowered out the character flaw out to make her role more interesting. And it makes a darn good scene when Jim finally discovers what's driving this wacky chick.
What is most criticized about this production is its clash of '30s and modern style. And sometimes, not even modern. It's more like Terry Gilliam's BRAZIL than anything human.
Yet the source novel itself is a good example of why this is not a bad policy. PICADILLY JIM came out in 1918. What was going on in 1918? Show of hands. That's right, World War One. Only a few years earlier, the steamship "Lusitania" was sunk by German U-boats. Yet in the book, there is no mention of the war that had been foremost on people's minds for years. Clubs and restaurants in London are populated by young men who are not shell-shocked or otherwise scarred from battle. They are the vapid but well-educated scions of the nobility who had been cannon fodder in the trenches for four years. Characters hop on steamships and go from New York to London and back to New York with no thought or mention of U-boats, mines, or other hazards to shipping.
Therefore, nearly one hundred years after this novel was first written, it does not seem bound to its time. Oh, the idea of traveling to England by steamship may be passé, but readers are not bogged down by the time-specific angst that makes so many "lost generation" novelists unpalatable today. Apart from a few mentions (such as in the novel QUICK SERVICE) no World War One intrudes into Wodehouse. Later on, though Wodehouse was in a German interment camp, England does not endure World War Two and his characters experience neither shortages nor bombings.
Nevertheless, though his characters seem stuck in their Edwardian pleasaunces, they do travel through time and keep up with certain new developments. Updating the book to the thirties made a lot of sense, but throwing in modern styles, while jolting in a Brazilian sort of way, also is not unWodehouse.
Warning: some unWodehouse things do appear, so strap in and be ready for them.
For an even more astute version of Wodehouse, see "Heavy Weather" with Peter O'Toole and Samuel West.