Paul is a road movie, indulging on the tried and true methodology of making the journey taken by characters into something very literal. Two friends played by Simon Pegg and Nick Frost are living out one of their longtime dreams by journeying from their homeland England to attend the San Diego Comic-Con and then journey across the U.S. in a rented R.V., stopping at famed locales connected to U.F.O.’s and alien visitations. Along the way, they encounter an actual space alien, a diminutive, foul-talking fellow who looks a little bit like Gumby turned anemic. Named Paul, the extra-terrestrial has escaped from the government facility where he’s been sharing scientific secrets and plotting the course of science fiction media for decades. Now he wants to return to his home planet and enlists the two genial blokes he’s met to get him to the place where his mother ship is expected to retrieve him.

This is the same sort of mutual embrace and spoof of genre that informed the prior Pegg and Frost team-ups Shaun of the Dead and Hot Fuzz. Where those films were built upon the well-built mechanics of the genres they targeted, Paul is a looser, goofier affair. The characters may be traveling the highways of the American West, but this is really a road trip through American movies. There are references to a multitude of other films; sometimes overt, sometimes sly, sometimes merely visual echoes stitched in seamlessly enough that significant portions of the audience will never spot the allusion. The affection felt for the material by Pegg and Frost, co-writers of the screenplay, is always clear. It has the same ticklish geeky wonderment of their old series, Spaced.

What the film is lacking is the inspired energy brought by Edgar Wright, director and co-writer of both Shaun of the Dead and Hot Fuzz. He may have occasionally hit too hard with the kinetic imagery, but he had a point of view and a keen sense of pacing. Instead Greg Mottola brings a similar deadpan blandness that worked well enough for Superbad and Adventureland but drags on the proceedings here. The film is too often perfunctory instead of gleeful, lacking the sort of happy-go-lucky exuberance that the plot cries out for. The other buddy films built around Pegg and Frost absolutely wallow in their genial, flinty nerdiness, but Mottola instead wants to drift above it. It’s still funny and nicely written, but missing the relentless charm of the earlier efforts. That’s the difference between a decent comedy and a fine film.