There's a reason for calling this brand-name sequel mindless entertainment. If you think about what you just wasted two hours watching, you won't be entertained anymore. Lethal Weapon 3 offers mediocrity wielded by experts. It's not a movie, it's a machine. Why a third time? The first movie earned $65 million, and the second more than doubled that. End of discussion.

Mel Gibson is back as Martin Riggs, the cop who was suicidal over his wife's death in part 1 but has become just a laughably nutso…