One of the best known movies of the 1980s - made before Mel Gibson became so weird, people are apparently now arguing for this as one of the defining moments in the development of the action movie genre.
Roger Murtaugh (Danny Glover) has just passed his 50th birthday - and been reminded several times by family and co-workers how old he is. He's assigned new partner Martin Riggs (Gibson), an ex-Special Forces soldier turned cop who's become suicidal after the death of his wife two years previously. Murtaugh is contacted by an old Vietnam war buddy and current banker, who wants him to look into the death of his daughter - which turns out to be linked not only to the pornography she was obviously involved in, but also a drug cartel. Rigg's suicidal tendencies makes him handy in dangerous situations - he'll walk right into a gunfight without caring. Of course that also tends to make him a bit dangerous to his partner.
I think of "Lethal Weapon" as an Al Leong movie that happens to star Gibson and Glover. Al Leong was infamous through the 1980s as a bit part player, the Asian martial arts sidekick (usually non-speaking roles), rocking the long-hair-going-bald look and a Fu Manchu moustache ... in this movie he actually speaks!
The movie wanders a bit erratically across the landscape, but Glover and Gibson enjoy a surprising and very entertaining chemistry that moves the movie along nicely.