I think Eastwood tried to make it more of a character driven story, it's the first and only time you ever really see Harry getting into a relationship in any detail ("Try knocking on the door" doesn't really count...) and it's certainly much darker than the others. Like I said, it's got a very different feel to it but that doesn't necessarily make it a bad film, I think it's good that someone at least tried something different, at least once.
But you're right in one aspect, Sondra Locke is awful but then she was Eastwood's Linda McCartney at the time and that's really insulting to Linda McCartney...