Coming off of two epic Paul Thomas Anderson films, with the demanding Her and The Immigrant in between them, Joaquin Phoenix seems due for a reprieve from heavy drama, which is what a Woody Allen movie sounds like. Unfortunately, or perhaps just characteristically, for Phoenix, Irrational Man proves to be Allen's darkest and least joyful film in a long time.

Phoenix stars as Abe Lucas, an alcoholic philosophy professor who comes to the small, fictional Rhode Island college of Braylin preceded by a reputation. Students and colleagues are both intrigued and concerned by the oft-disheveled new faculty member. Married science professor Rita Richards (Parker Posey) takes an immediate interest in Abe, wooing him with a bottle of Scotch. Meanwhile, Abe makes an admirer out of Jill Pollard (Emma Stone), a student of his who can't keep gushing about him to her boyfriend (Jamie Blackley) and parents.

The potbellied Abe -- whether or not the previously gaunt Phoenix gained weight just for this role, the camera accentuates his unhealthy physique -- resists Jill's romantic advances and is unable to perform for the forward Rita. Despite all the principles he's taught and written about, he's sleepwalking through life, struggling to see meaning in anything. Until one day, while dining with Jill, he overhears a group in the neighboring booth discussing a mother's upcoming custody battle. The eavesdropping is enough to convince Abe that the world would be a better place if that mother's assigned judge were no longer alive. Abe himself suddenly feels alive, plotting the undetectable murder of a perfect stranger, which he sets out to commit after observing the judge's routines.

Irrational Man is a bit of a slog. It starts promisingly enough with some lovely sunny photography by Allen's now frequent cinematographer Darius Khondji. A few multi-dimensional characters are introduced and developed, the distance in age and outlook of our leading man and lady generating some interest. But Phoenix shows little interest in simply being the latest in a long line of Woody Allen surrogates. Abe's appeal to students and staff members alike is part joke, part mystery. He is not an easy character to warm to, nor are others who see him as some enlightened guru.

Like the protagonist, the movie picks up a bit when stepping away from the non-pressing love triangle established in the complacent first act. Abe's sliding morality scale makes for a more compelling study than any one of these characters or their relationships and it's easy to get caught up in his descent into stealth murderer, the viewer uncertain he has what it takes. The material does recall Allen's 1989 drama Crimes and Misdemeanors, which itself harks back to Hitchcock's Strangers on a Train. Irrational doesn't have much new of interest to share on the subject and the second half of the movie truly belabors this plot, slowly exposing Abe's transgressions one minor detail at a time. The film is also plagued by an overreliance on voiceover narration, a design that is clunky and unusual for Allen.

If tied to characters we cared deeply about or a target who didn't arise out of a contrived, random diner conversation, this story might stir and move. Instead, it's tempting to classify this work as one of Woody's lesser efforts and one that might put an end to theories that the productive filmmaker is alternating between good movies and mediocre ones in his clockwork-like annual output. Irrational Man is a small step down from last year's underappreciated comedy Magic in the Moonlight and a bigger downgrade from Allen's most decorated and best-performing films of this decade, Midnight in Paris and Blue Jasmine.

Even so, it's important not to overstate the film's missteps or to overlook the sheer creativity Allen has shown on a yearly basis in telling his all-original tales with such varied settings and personalities. Though it may ensure him a built-in audience, Allen's legacy may work against him when it comes to critics, who may find it more interesting to declare Allen's best work long behind him than to paint the more accurate picture that his hit-and-miss works generally occupy a narrow range between the mediocre and the best of new films. Irrational Man is not short on substance, but it does not make the lasting impression of the writer-director's better efforts.