Oliver Parker, who directed and wrote the screen adaptation, simply misinterpreted the play. He focused on the "dashing young bachelors" when the real focus of the play is Lady Bracknell, the absurd and beautifully ironic representation of the Victorian mind who was then and has been for over a hundred years Wilde's singular creation and one of the great characters of English literature. She is supposed to steal every scene she is in and we are to double take everyone of her speeches as we feel that she is simultaneous absurd and exactly right. Instead Judi Dench's Lady Bracknell (and I don't blame Dench who is a fine actress) is harsh and stern and literal to the point of being a controlling matriarch when what Wilde had in mind was somebody who was both pompous and almost idiotic yet capable of a penetrating and cynical wisdom (so like the author's). Compared to Dane Edith Evans's brilliant performance in the celebrated cinematic production from 1952, Dench's Lady Bracknell is positively one-dimensional.
The point of Wilde's play was to simultaneously delight and satirize the Victorian audience who came to watch the play. This is the genius of the play: the play-goer might view all of the values of bourgeois society upheld while at the same time they are being made fun of. Not an easy trick, but that is why The Importance of Being Earnest is considered one of the greatest plays ever written. This attempt turn it into a light entertainment for today's youthful audiences fails because this play is not a romantic comedy. It is more precisely a satire of a romantic comedy. Its point and Wilde's intent was to make fun of Victorian notions of romance and marrying well and to expose the mercantile nature of that society. It is probably impossible to "translate" the play for the contemporary film viewer since a satire of today's audiences and today's society would require an entirely different set of rapiers.
Parker's additions to the play only amounted to distractions that diluted the essence of the play's incomparable wit. Most of Wilde's witticisms were lost in the glare of Parker's busy work. Recalling Lady Bracknell as a dance hall girl in her youth who became pregnant before being wed was ridiculous and not only added nothing, but misinterpreted her character. Lady Bracknell is not a hypocrite with a compromised past. She is everything she pretends to be and that is the joke. Showing Algernon actually running through the streets to escape creditors or being threatened with debtor's prison was silly and again missed the point. Algy was "hard up" true and in need of "ready money" but his bills would be paid. Gwendolyn in goggles and cap driving a motor car also added nothing and seemed to place the play some years after the fact.
The big mistake movie directors often make when making a movie from a stage play is to feel compelled to get the play off the stage and out into the streets and countryside. Almost always these attempts are simply distractions. Some of the greatest adaptations--Elia Kazan's A Streetcar Named Desire from 1951 comes immediately to mind--played it straight and didn't try anything fancy. Here Parker seems obsessed with "dressing up" the play. What he does is obscure it.
On the positive side the costumes were beautiful and Anna Massy was an indelible Miss Prism. Reese Witherspoon at least looked the part of Cecily and she obviously worked hard. Rupert Evertt had some moments in the beginning that resembled Wilde's Algernon, but he was not able to sustain the impersonation.
My recommendation is that you not bother with this production and instead get the 1952 film starring, in addition to Edith Evans, Michael Redgrave and Margaret Rutherford. It is essentially true to the play as Wilde wrote it, and is a pure delight.
(Note: Over 500 of my movie reviews are now available in my book "Cut to the Chaise Lounge or I Can't Believe I Swallowed the Remote!" Get it at Amazon!)