The party line on Tony Richardson's 1963 adaptation of Henry Fielding's Tom Jones is that it is a period film done up in the style of the French New Wave, which is a little bit accurate and a whole lot reductive. It's an easy point to forget that there were many styles of filmmaking in the 1960s that weren't the French New Wave (hell, there were even New Waves that weren't French), and Tom Jones is equally indebted to them all. Put it another way: to see what a British take on the New Wave aesthetic looks like, take a peek Richard Lester's A Hard Day's Night from the following year, but Tom Jones is more like a snapshot of the state of Euro-American filmmaking, c. 1963.
Consider: it opens with a short prologue setting up the film's backstory done as a silent film, something that feels mostly like British slapstick of the time, though Godard and others in France played around with silent aesthetic. The casting of Albert Finney in the title role (supposedly after he decided that playing Lawrence of Arabia would be too much work) is a clear nod to the Angry Young Men realism just poking its head into the realm of cinema. The camerawork is clearly most in line with the work being done by the most adventurous Hollywood filmmakers at the time: a great deal of handheld filming, extensive helicopter shots (the film's most unsettlingly radical choice; being that this is the 18th century, those helicopter shots are of things like fox hunts, and even today it completely subverts our expectations for how such things "ought" to be filmed), and plenty of crash zooms. Even the film's tone, that of a naughty but not licentious sex farce, is surely indebted to the new sexual freedom explored by directors like Ingmar Bergman and Federico Fellini (and would become something of a stock genre in Britain over the course of the decade). Probably the only ways in which Tom Jones is clearly influenced by the New Wave and only the New Wave are those in which the film announces its "film-ness" to us most strongly: its use of direct address, clipped editing rhythms, and the fact that at least the lead character seems to be aware that he is in a movie. Though come to think of it, the typical New Wave protagonist didn't know that he was in a movie; he wanted to be in a movie.
As full of the movie is of time capsule stylistic elements - and my whirlwind tour was just that, a tour, for the whole movie is a collection of influences and references - it's fair to say that Tom Jones is extremely dated, though not in a detrimental way e.g. Easy Rider where the film's value seems to have all been spent after its moment in history passed. Rather, it's obvious that this film could only have ever been made in a span of few years, probably only in the country where it was made. Though it remains funny and entertaining (and it probably enjoys a stronger reputation than the four films it beat for the Best Picture Oscar), it's impossible to watch the film without being aware that it is from 1963, according to every signifier that you can use to time-stamp a motion picture.
And yet (as there must always be an "and yet"), it still feels somewhat fresh and unexpected to the modern viewer, simply because it isn't really like any film released in the intervening 45 years. With the very rare exception like Sofia Coppola's Marie Antoinette, costume dramas that look and feel like contemporary movies are extraordinarily unusual,* for even today we expect that films set prior to the invention of electric lighting should be fussy and stuffy and chock full of people with British accents wrapping their mouths around sentences with eight clauses. To be fair, there's some of that in Tom Jones, but used in a very particular way: all of the characters who represent the Proper Aristocracy, opposed to Tom's mischievousness, behave like Masterpiece Theater stock figures (David Warner as Tom's rival Mr Blifil, Peter Bull as the censorious religious tutor Mr Thwackum), while those more inclined to indulge Tom are a bit more silly and modern in representation (his adopted father Squire Allworthy, played by George Devine, Hugh Griffith's marvelous turn as the gaudy Squire Western), right up to the young punks who don't give a damn about propriety, acting like they just stepped out of a Dick Sellers comedy - Finney's Tom of course, or Susannah York as his love Sophie Western.
Tony Richardson's goal in wrapping the most modern techniques around the young radicals in his film could hardly be more obvious: Tom Jones is a manifesto for a new direction in British performing arts, carried forth by the young Turks who stand in direct opposition to the emotionless propriety of their parents and their parents' parents. Historically, British cinema has always been one of the most conservative in the world (think ahead to the infamous Video Nasties period, when a film's rental success in the US or Europe could hinge on having the "Banned in Britain!" sticker on its video box), but that country produced some of the most socially confrontational films made between, let's say, 1962 and 1971 or so. Richardson has made a microcosmic study of the cultural warfare soon to explode in films like The Knack, if... and A Clockwork Orange, clearly agitating on behalf of the new and the young.
That said, there's another and perhaps more objectively satisfying reason why Tom Jones should be so vibrant with the experimental spirit of the 1960s. It bears remembering that in 1749, Fielding's The History of Tom Jones, a Foundling wasn't the dusty classic that nobody reads today. It was yet another in the long line of scandalous books filled with all sorts of immoral, un-Christian naughtiness that now fill the backbone of the English-language literary canon, and was devoured by the masses even as it was denounced for its filth. We tend to forget that part when we think about old novels, treating them in film adaptations like museum pieces for the enjoyment of stodgy, mirthless prudes. Richardson's innovation was to make a Tom Jones for 1963 that would have the same impact as Fielding's did over two centuries earlier. Coy without being shocking and just scandalous enough that everybody would be talking about it, the film is one of the only examples I can name of an adaptation that actively seeks to recreate the details of its source novel's reception.
It makes for an in-the-moment bit of playfulness that more modern costume dramas might be well-advised to consider; I might also like to put it in a double-feature with its antithesis, Stanley Kubrick's masterful Barry Lyndon as the two extreme poles of the genre, and two of the best films ever produced in the form. Though it isn't as avant-garde as it was at the time of its birth, it's still unexpectedly light and energetic, and a classic not just of literary adaptation, but of the last truly adventurous era in British and European filmmaking.