Ghost Town, David Koepp, 102 mins, 12A Quiet Chaos, Antonello Grimaldi, 112 mins, 15

You can take the boy out of Slough ...but you can't put him in a shiny New York screwball comedy. Ricky, you should have a word with your agent

Now here's a funny thing. Two films open this week, both about death and mourning, both starring funny men out of their usual contexts, both advertised by posters showing the star sitting on a bench. As Harry Hill might say, what are the chances of that happening?

Come to think of it, Harry Hill might have made a better casting choice for David Koepp's comedy Ghost Town, as indeed would any exportable British comic: Steve Coogan, Eddie Izzard, Sacha Baron Cohen, anyone other than Ricky Gervais. More than any comedian I can think of, Gervais's appeal depends on context. When he plays a self-created character such as David Brent or Andy Millman, he's in control of the role and the situation, and able to surround himself with supporting players that lend credibility to both.

Now, you can believe in Gervais as a white-collar worker in Slough, or an actor whose sitcom becomes an albatross. But as a dentist in uptown New York? I think not. For one thing, look at the man's teeth: he wouldn't attract the clientele. That's not the only reason that Gervais doesn't convince in Ghost Town: another is that his character is called Dr Bertram Pincus, which means the film's battle is lost from the start. Gervais's agent should have held out for a manageably run-of-the-mill name, but I suppose Koepp couldn't bear to sacrifice his running gag about people calling him "Pink-ass".

Ghost Town is a glossy, derivative package – The Sixth Sense meets A Christmas Carol by way of Bringing Up Baby – that plays Gervais's bumbling sourpuss against a classily ditzy broad, a Katharine Hepburn role filled by Téa Leoni as an expert in mummies. The morose, misanthropic Dr Pincus temporarily dies during a colonoscopy (and seriously – you have to be Larry David to get laughs out of colonoscopy), then begins to see dead people. One of them is Frank (Greg Kinnear), an obnoxious playboy who dies in a tux, and so looks consistently dapper for the rest of his afterlife.

Frank entrusts Pincus with a mission – dissuade his ex-wife (Leoni) from remarrying. Pincus falls for her and decides to win her love, but must first persuade her that he's not the abject jerk he so obviously is. That hollow creaking you hear as I write these words could be the gears of Koepp's script, or Gervais's jaw as it settles into its familiar cheese-eating grimace. Or it could be Howard Hawks and Preston Sturges rising from their tombs to exact revenge for Koepp's shoddy misuse of the screwball tradition.

Ghost Town is not entirely without panache; it's just that it's the wrong kind of panache for Ricky Gervais. The film is a sleek factory product, and its American actors have the snappy confidence that sometimes makes such products work. The moment Kinnear walks on, breezy and abrasive, giving it the old Jack Lemmon chin, you know you're dealing with a pro. Likewise, Kristen Wiig's surgeon, who partners Gervais in an engaging routine where they confusedly volley fragments of unfinished sentences.

All this is not to say that Gervais isn't in their league – just that he's in a different league. His moany, ingratiating floppiness doesn't gel in this brash, buffed context: it's like serving hake and chips in a sushi bar. Surround him with people such as Stephen Merchant or Ashley Jensen, with whom he shares rhythm and a set of social references, and Gervais works a treat. Casting him here makes no more sense than, say, importing Phil Silvers for a Carry On film. (They tried it: catastrophe.)

Gervais could learn about the art of being dyspeptic from Italian actor-director Nanni Moretti, whose air of aggrieved mystification was the backbone of his very personal comedies Dear Diary and Aprile. Moretti has co-written but not directed Quiet Chaos, in which he plays Pietro, who reacts to his wife's sudden death by abandoning work and planting himself on a bench opposite his daughter's school. There's no grand emotional redemption at stake, no narrative string-pulling, just a gentle, persuasively loose evocation of a man piecing his life together after grief has thrown it into jigsaw confusion. Characters from Pietro's life come and go – work colleagues, jeans-designer brother, neurotic sister-in-law (a magnificently frazzled Valeria Golino) – and it all seems a hazy swirl, but Moretti holds it together with his sardonic composure.

Quiet Chaos is too close to Moretti's own Palme d'Or-winning bereavement drama The Son's Room (2001) to feel remotely fresh. But it's intelligent, likeably baggy and elegantly directed by Antonello Grimaldi. The only false note is a supposedly cathartic sex scene, which has a dated air of upmarket Euro softcore. And to be perfectly candid, I can't think of anyone whose bottom I less want to see on screen than Nanni Moretti's. Except, obviously, Ricky Gervais's; at least Ghost Town spares us that.