I recently rewatched 3 and 4 cause I just got a wild curiosity. It had been a while. LW3 is easily my least favorite, as they sort of sacrifice the Riggs/Murtaugh dynamic for Rene Russo, and it has the weakest villains of the series. Stuart Wilson? That's when you really can't land anyone else.
LW4 is sappy, and as usual, they recycle and run into the ground all of the bits from the previous incarnations. Pesci's "froggy" speech is painful, and it's sappy as hell, but I still enjoyed it a bit. Jet Li is disappointing if you've seen his HK stuff, but they still gave him a nice intro for US audiences. They play up his moves, his speed, and unlike his other Silver pictures, Donner doesn't cut the hell out of his fight sequences. The final three way fight is actually brutal, believable, and pretty damn good.