Run Fatboy Run is a paradox: it is a pretty good movie that is not good at all.

Basically, the situation is that a team of really fine actors, led by the entirely reliable Simon Pegg and the desperately under-appreciated Thandie Newton are out there giving really solid performances in a script by Pegg and Michael Ian Black of The State and Stella that is, if not profoundly imaginative, a perfectly effective bit of craftsmanship moving from here to there; cinematographer Richard Greatrex captures some nice footage of a local's view of tourist London that makes the city look both like and unlike it looks in most movies; and in a pleasant surprise if I ever saw one, middling sitcom actor David Schwimmer, making his directorial debut, turns out to possess extreme competence in his filmmaking style: he keeps scenes moving briskly, he has a fine eye, his blocking is efficient and effortless. The very worst thing you can say about him is that he has a predilection for trite musical choices on the film's unusually bloated soundtrack.

In short, Run Fatboy Run is a fine work of craftspeople both in front of the camera and behind, whose collective ability to tell a story crisply and believably is entirely beyond question, and whose chief mistake is that every one of them appears to have forgotten that the story they were telling was in fact a comedy. Well-made it is, funny it most conspicuously is not.

The situation: on his wedding day, Dennis (Pegg) becomes incredibly panicked and runs, leaving his fiancée Libby (Newton) at the alter. Five years later, he's become a pudgy (though by no reasonable standard a "fatboy" - this is an actor best known for his work opposite Nick Frost, for God's sake) security guard and she is a single mother happily receiving the courtship of a fit, smart, rich, clever American named Whit (Hank Azaria). Yada yada yada, Dennis decides that the only way he can win Libby back is by besting Whit in the first ever "Marathon Across London That We Invented for the Film."

Is the seed for a perfectly charming time-waster planted in there? Sure. The frustrating thing about Run Fatboy Run is how desperately close that seed comes to germinating. There's a really good cast in place (the fourth ingredient, as Dennis's best mate, is Pegg's Shaun of the Dead costar Dylan Moran), and it looks for all the world like Schwimmer is pacing the film exactly the way that a breezy comedy ought to be paced. It's just that the gags - which are entirely recognisable as gags, structured with punchlines and everything - aren't played like gags. I'm not suggesting that those good actors need to go around mugging every time something funny happens, but they play it so straight, according to the dramatic needs of of their characters, that it comes across like Kramer vs. Kramer: Zany Edition, with quick-witted drama taking the place of humor. The best I can say is that it feels like a comedy made by people who have never encountered the idea of laughter.

That's a crippling enough flaw that the film hardly needs another, but I've got one anyway: its cultural specificity is all shot to hell. Black wrote the story to take place in Los Angeles, but sometime in its development it ended up in England with Pegg stepping in to rewrite the script for his country. Which is just fine. But the English-ness of the film feels weirdly forced given how much of the cast and crew is from Great Britain, and the American-ness pokes out too often. Everything that's British is in the trappings, but not in the heart - compare Pegg's Shaun of the Dead, which is British to the core. Run Fatboy Run has British bands on the soundtrack, but characters mouthing American idioms; famous London buildings surrounding transplanted Angelinos with accents. The closest thing the plot comes to an Essentially London experience is the subplot concerned with the Lord of the Rings musical that already makes the film feel as ancient and dated as a '60s sex farce. (Yes, the show is still running. Somehow, that doesn't seem to matter).

Anyway, the film is a bland disaster, and that's without noting it's deeply illogical third-act problems (it's a film about an underdog who trains to be the best he can be, and yet I was still broadsided by the terrifyingly inorganic "inspirational" climax). It is cute and silly and sweet and juvenile, and it is all of those things without ever once being amusing. There doesn't seem to be much else to say about it. If it bends, it's funny; if it breaks, it isn't funny; if you just stare at it without even trying to bend it, it's Run Fatboy Run.