Showtime stars Robert De Niro and Eddie Murphy as two Los Angeles cops who keep stepping on each other's toes -- De Niro is an efficient sergeant trying to organise complicated drug busts, Murphy is a doofus patrolman who keeps getting in De Niro's way through unfortunate coincidences. Into the plot comes a tabloid producer played by Rene Russo, who decides that these two should be paired up for a reality TV show.

Of course the big captain goes along with this for some silly reason, and leaves the two guys to butt heads -- De Niro is a tight-lipped tough guy who doesn't want any part of Hollywood games, while Murphy wants to be a star so badly that he springs into weepy speeches in everyday conversation and tries to turn the end of every sentence into a catchphrase.

These are obvious comic roles, but De Niro and Murphy are great actors, and it's interesting how instead of merely bugging his partner, each man has fundamental disrespect for the way the other approaches his job. De Niro thinks Murphy is a joke of a cop, fooling around in a way that's likely to get someone hurt. Murphy is one of those shallowly happy-go-lucky twits who just can't understand why so many people are grumpy all the time.

The first hour of Showtime is broad and silly, but amusingly satirical. There is witty, contemporary dialogue (a studio exec looks at his office computer and moans, "I just got outbid for this 'A-Team' lunchbox on eBay!"), and such features as a cameo appearance by Johnnie Cochran, who sits with a client in police custody and informs the cops, "If he don't talk, we walk!" The cast is fun to watch, and I like how the TV producers keep saying they're going to keep their show real as they rip apart locations to suit the camera.

The last third, however, descends into unapologetic cliché. "I've never caused a chain reaction car pile-up, I've never been chewed out by my boss for being a loose cannon," says De Niro in the opening scene, and yet the movie does turn into a string of action set pieces and gun-and-badge scenes. Showtime makes a joke out of car chases for an hour and then gives us half an hour of car chases, and it's not irony, it's laziness. This is the kind of movie best watched on television, where you can glance at the good bits and ignore the junk.

(Review also posted on http://www.ukcritic.com.)

Released by Warner Bros. and rated "PG-13" for action violence, language, and some drug content.