Val Kilmer’s name on a film poster is, these days, enough to drive anyone away. He’s been associated with more high-profile duds than pretty much any actor currently working, be it the awful The Saint to the sprawling Alexander, has built up a reputation for being an arrogant and unpleasant person to work with, and by most accounts he hasn’t managed to put in a genuinely good performance since 1993′s Tombstone, where he was truly superb as the slowly dying gunslinger Doc Holliday.

Robert Downey Jr has likewise not had much luck in recent years. Though he won wild praise for his turn in the title role of Richard Attenborough’s ambitious biopic Chaplin back in 1992, for the past decade or so he’s been more prominent in the tabloids for drug offences and imprisonment than for anything he’s managed to achieve in front of the camera, and is probably best known these days for being in an Elton John video and playing yet another in a long string of Ally McBeal’s boyfriends.

Putting these two together as the headline leads in a movie is, therefore, either utterly insane or a very bold move, depending on how much faith you have in their abilities to shake off their respective reputations and actually start to bother acting again.

Written and directed by the screenwriter behind the insanely successful and continually endearing Lethal Weapon series, the news that this is another take on the “mismatched men have to overcome their differences to solve a crime” idea that lies at the heart of that franchise might also suggest a certain lack of originality.

The fear might be that this is merely a rejected script for Lethal Weapon 5 that Mel Gibson didn’t want anything to do with now that he’s not only richer than God but in the big man’s good books for The Passion of the Christ to boot.

Somehow, though, this combination of talent with chequered pasts has merged to bring out the best in all concerned. Though there may be little logic to the plot, centred around Downey Jr’s petty thief trying to make it as an actor in Hollywood under gay detective Kilmer’s tutelage amidst an LA underworld that becomes increasingly strewn with bodies, the two leads are both back at the top of their game.

This kind of movie, undoubtedly a buddy cop film in the fine 1980s tradition of Lethal Weapon, 48 Hours and Beverley Hills Cop but with a noughties twist, succeeds purely on the charisma and on-screen relationship of the lead actors.

With Downey Jr and Kilmer on top of their game, as they are here after a long famine of good roles, even with the most ridiculous premise the movie would work. They both, when on form, can exude such an easy presence and charm that either alone could buoy up an otherwise poor movie. Neither has done so for such a long time, the sight of both working expertly together is a real joy.

This is by no means an excellent movie – it’s a bit too silly to become that. It is, however, great fun, solidly entertaining, and a long-overdue return to form for two of Hollywood’s finest bad boy actors. More than worth the price of admission.