I don't suppose Diary is much known in the United States; at least I had never heard of it until I went to London and found a few copies in almost every bookstore. They seem to treat it as kind of a national ornament, the same way the Czechs treat The Good Soldier Schweick.
I'd say that Bonneville does a fine job of capturing the spirit of the piece in this "performance" which is, in fact, not a lot more than an extended dramatic reading. Diary, as I understand it, qualifies at least as a period piece: an account of the new consciousness of a new class (lower middle, clerical) prosperous enough to move to new suburbs (Upper Holloway--Archway, North Islington, N19), made accessible by the greatly expanded network of public transport. As Wiki says:
The humour derives from Pooter's unconscious gaffes and self-importance, as well as the snubs he receives from those he considers socially inferior, such as tradesmen. The book has spawned the word "Pooterish" to describe a tendency to take oneself excessively seriously.Turned round, this is one of the most mean-spirited items in the history of British comedy since the death of Tobias Smollett. I grant that Pooter does observe himself with a measure of reverence but he is also hard-working, steady, kind, and loyal to his loved ones. It takes a fully developed impulse for snobbery to look down one's nose at someone who actually thinks he ought to nick off a few middle class comforts as his own (Bonneville gives him a Cockney accent; a bullseye tipoff that he is living beyond his class). It says something about Britain that it has proven so durable and so (can I say this?) much loved.