As the Lethal Weapon series becomes an increasingly cartoonish self-parody, the jokes get about as tired as Danny Glover's wheezy sergeant Roger Murtaugh. A proven formula is what allows a franchise to grow old and gray, but Lethal Weapon 3 milks the funny moments of its predecessors so shamelessly that it's head-scratching. The squabbling buddy cops Riggs (Mel Gibson) and Murtaugh are still arguing over who gets to drive, how to count to three, and whether Riggs should dive headlong into extreme danger, often without a weapon, with the kind of zeal borne of knowing he's under contract for a fourth installment. Gibson and Glover have a chemistry that's fun to watch, and are blessed with the zippy timing of a good comedic partnership. And maybe that's enough, as director Richard Donner seems to choose this point in the series to switch from action to comedy, leaving behind the darker brooding qualities of the first two in favor of even more vestigial schtick from Joe Pesci. (A dead giveaway that this is all a big joke: the events take place in Murtaugh's final week before retirement.) It certainly doesn't score as an action movie -- there's little to get excited about among the succession of generally unrelated set pieces involving fisticuffs, car chases, and gun battles. The wispy plot about a crooked cop-turned-gun-runner exists mostly to lend righteousness to Murtaugh, who guns down a gangbanger his son's age during a shoot-out with said illegal weapons. Rene Russo becomes a series regular, and provides additional banter as well as some kick-ass moves. But the larger the ensemble gets, the more unwieldy the results.