His last movie was Parting Shots in 1999. Never saw it, but by all accounts it was pretty bad, as is much of his later work.
He made a few reasonable movies in the sixties and seventies, like Hannibal Brooks, Scorpio, The Mechanic, and to a certain degree Death Wish.
But I find him a very bland and anonymous director, he has no sense of style whatsoever, he simply points the camera and shoots. No flair, nothing to mark him out as an individual.
And after Death Wish, he really made some dreadful movies. His nadir for me is Bullseye, a terrible comedy with Roger Moore and Michael Caine. He seemed to fall into making dreadful exploitation movies, often returning to the Death Wish theme (he made two sequels, the dreadfully lurid Death Wish 2, and the entirely unconvincing London based 3, which was supposed to look like New York) with movies like Scream for Help and Dirty Weekend.
Nope - I am afraid he would be on my list of worst directors.
And of course these days he seems to have thankfully given up making movies altogether...though I am not sure those awful tv adverts are any better...