Larry Crowne (12A) / The Conspirator (12A) 2/5, 2/5

Watching the romantic comedy Larry Crowne is like listening to someone tell a very long but harmless joke. It's sweet that they've tried, but it's a little bit tiresome having to sit there and feign laughter. Its writer, director and star is Tom Hanks, one of Hollywood's most bankable – and most neutered – of actors. With one or two exceptions Hanks has never really stretched himself since his two Oscar wins of the 1990s (for Philadelphia and Forrest Gump), when he settled for being the modern Bing Crosby. If pipes and plaid slippers were still in fashion, he'd be sporting them.

His Larry Crowne is an American Everyman, a decent blue-collar guy who works at the local U-Mart. Summoned to the office one day expecting another Employee of the Month award, he learns instead that he's being fired, because his promotional prospects are "forever retarded" by his lack of a college education. Devastated, Larry binges on drugs and booze, loads up a shotgun and – no, just kidding there. He actually gets a job in a local diner (he was once a cook in the Navy) and enrols at a community college to get the qualifications he missed out on. There he is befriended, somewhat incredibly, by a sassy young student, Talia (Gugu Mbatha-Raw), who oversees an all-points makeover – out go his drab middle-aged duds and SUV, in come a cool haircut, a Vespa, a new lease of life.

Were this a risky, interesting film, Larry might pursue Talia – who's flirty, beautiful and black – crossing the barriers of age and race perhaps to find himself an outcast, or a daring romantic. No dice. Instead it goes for the much easier fantasy of his falling for his college professor, who just happens to be (brilliant!) Julia Roberts. She is Mercedes Tainot, utterly disaffected with her job and her marriage to a blogger who watches internet porn all day. She douses her disappointment in a nightly margarita, which the film weakly suggests is a drink problem, though what the sleazy husband actually complains about is her lack of "knockers". Conveniently, he's soon out on his ear, and the way is clear for her and Larry to hook up. But likeable as Hanks and Roberts are, their romance is a fizzle, a starchy and unsensual liaison between two people who seem to have very little in common. Hanks still plies his puppyish charm (he's an older dog these days) while Roberts's big, dirty laugh rings false – there's no occasion for it.

As a writer-director, Hanks looks out of practice (his last effort was That Thing You Do!, a pleasant 1960s pop pastiche from 1996). The pacing is dozy and the characterisation offhand to the point of negligence. We find out little about Mercedes's husband beyond the porn habit, and nothing at all about Larry's ex-wife. The banter among the minor characters and the larks of college life lack any sharpness of observation, for which Nia Vardalos, Hanks's co-writer, must also carry some blame. Of course, you can't really object to the likes of Tom Hanks and Julia Roberts: they will never do less than a professional job. But the film they're attached to is blander than a milkshake and soppier than a Hallmark card.

Robert Redford is, like Hanks, a Hollywood untouchable who's always wanted too badly to be loved. His latest film as director, The Conspirator, is a lavishly mounted but ponderously composed "lesson from history". In the aftermath of President Lincoln's murder in April 1865 the authorities arrested Mary Surratt (Robin Wright), a Southern Catholic widow and owner of a Washington boarding-house where several conspirators, including John Wilkes Booth, had stayed. Answering the country's fearful mood, a military tribunal rather than a jury of her peers is set up to try Mrs. Surratt, whose son John was among the plotters. Was she herself involved in it, or merely guilty by association?

That is the question young defence attorney Frederick Aiken (James McAvoy) must solve in a second half that flips between the courtroom and flashbacks to the Surratt family's recent past. What's curious and baffling about James Solomon's script is its greater interest in Aiken than in his client. We see how the young man, himself a Union war hero, must run the gauntlet of a vindictive War Secretary (Kevin Kline), a savvy prosecutor (Danny Huston) and the general opprobrium of a public thirsting for revenge. Even his friends can't understand why he's backing a loser. That's because they haven't the benefit of liberal American hindsight. Redford, as he did in his previous Lions for Lambs, is giving his audience a talking-to about the constitution: namely, that it must be upheld for all citizens, at all times. The parallels with the present – hooded prisoners, military-style justice – are underlined with emphatic piety.

A mythic mist of sepia overhangs all, with a golden light flooding through the windows like an American Vermeer. It lends the film the air of a reconstruction, tasteful yet pretty savourless. McAvoy is a perky bantam presence as Aiken, and Robin Wright, despite being dressed like Whistler's Mother, projects a sense of oppression nobly borne. Her cheekbones are eloquence itself. Sadly, she's been given hardly anything to say, and only at the very end, with a newly built gallows lowering over her, does The Conspirator deliver a blow that truly winds. Until then it's been mostly the comforting breeze of civics-class rhetoric.