I'm a fan of the private eye and film noir genres, and this is kind of both, and just a fine movie overall. Gene Hackman gives an understated and subtle performance as Harry, an ex-football player turned private investigator. His dialog is classic wise-cracking PI, and things start out as a straightforward detective story. But this movie tries to show that his profession is built on corrupt and shaky foundations (a little heavy-handedly).
Also dancing on the fine line between clever and annoying is the interplay between the movie's title and Harry's reference to "knight moves" in the chess game he's analyzing. The player he obviously identifies with had a win if only he'd seen the correct knight moves. Observes Harry: "He played something else and he lost. He must have regretted it every day of his life. I know I would have." And, sure enough, Harry misses his correct moves too.
This movie was made in 1975, and displays that era's more casual attitude towards showing boobies.