Lasse Hallstrom's comedy "Casanova" is good enough that one only wishes it were better. The surprising casting of Heath Ledger as Casanova - he's not, after all, a gorgeous hunk with great cheekbones and bedroom eyes but an actor who relies on his marvelous vocal range for his effects - helps the film, as does the casting of the attractive yet tough-looking Sienna Miller as his feminist foil. But the film moves in fits and starts instead of a smooth progression, and the script could have used one more rewrite to help it along.

The story, in this iteration, is classic Goldoni farce: Casanova is already legendary in his Venetian world for his 'conquests,' which look more like mutually beneficial nights than any kind of one-sided event: early on he's forced by the police to run from a convent where he apparently knows every sister by heart and body part, and when he's brought before the Doge on the charge of fornication with a novice, he mutters under his breath, "She was hardly a novice." If only the rest of the film were as good as that line.

But there is a lot that is good. Oliver Platt, the lard king of Genoa who looks as though he's been sampling his own wares, is Paprizzio, affianced to a young virgin whom Casanova covets. He covets her, that is, until he meets Francesca Bruni, writer of feminist tracts under a man's name and sister of the young, also virginal man who secretly lusts after the young virgin as well. Their cute meet takes place when she, dressed like a man, takes her brother's place in a duel with Casanova and, of course, wins his heart. The rest of the film takes us through the trials and tribulations of the pair as iconoclast, feminist and sexual liberal under the heel of the inquisition as represented by the spectre-like Jeremy Irons as Bishop Pucci, ready to throw anyone into the dungeon, or preferably to hang them.

There are escapes, mistaken identities and many disguises, and much of it is funny; but the film lurches when it should sail smoothly, and spends time with more characters than the plot really needs, including Francesca's mother (Lena Olin), who ends up with Paprizzio herself. I like neat endings, but I wish it were more fun getting there. Masters of cuisine say there's nothing like lard to make a feather-light pie crust, and this film is so light it almost floats away. All together now: One-More-Rewrite!