The British director Sally Potter seems always to be pushing boundaries, whether it's the notion of gender in her 1992 drama "Orlando" or now film itself in her new movie, "Yes." Ambitious, overweening, politically engaged, smug, lyrical and clunky, it's a mess but a sporadically beautiful one, with a searching tone and a willingness to take risks that viewers can't help but admire, even as they find it belabored and, ultimately, inert. It's a bold exercise, an interesting experiment, but a movie it ain't.

The bad grammar is used intentionally, as an antidote to Potter's hyperstylized, occasionally fatuous dialogue, nearly all of which is delivered in pseudo-Shakespearean iambic pentameter. Joan Allen -- who has had an unusually fecund run this year, delivering star turns in "Off the Map," "The Upside of Anger" and now this -- plays a character named She, an American living in London who is suffocating in her marriage to a wealthy politician (Sam Neill) and embarks on an affair with a Lebanese chef named, what else, He (Simon Abkarian). In the course of their liaison, He and She explore and embody almost every issue facing 21st-century humans, including science, spirituality, sex and the politics of science, spirituality and sex.

Allen and Abkarian handle Potter's verse with admirable dexterity, and occasionally the speeches touch a nerve; there's an encounter having to do with Middle East politics that is particularly resonant in light of recent events in London. But Potter packs way too much into what could be an elegantly spare story, adding a best friend, a goddaughter and a beloved aunt and sending the suddenly politicized She on a weirdly digressive journey to Cuba, via Belfast. (While in Belfast, She visits a dying aunt, who delivers one of the film's best monologues, a triumphant last cry of rage against the dying of the light.)

Thanks to the ministrations of cinematographer Aleksei Rodionov, "Yes" often takes on a painterly visual elegance, such as in a scene in which a housemaid (well played by the kitten-voiced Shirley Henderson) washes dishes at a sink, poetically echoing a print on the wall. But too often Potter succumbs to the use of slow motion and other gee-look-what-I-can-do effects, giving the whole endeavor the air of a precocious film school project.

The poetry, too, is often painfully bad, such as when Allen summons all her authority to declaim, "I did not mean to infer that you were overlarge!" Ouch. Potter might have benefited from the services of a good copy editor, or maybe just a trusted adviser who could tell her that good intentions, intellectual airs and artistic pretensions don't necessarily add up to good cinema.

Yes (100 minutes, at Landmark's E Street) is rated R for profanity and some sexual content.

As She, Joan Allen takes on a Lebanese lover named He (Simon Abkarian, below) in "Yes."