I saw it when it was new, in the theatre. Of course I'd gone to see my man Robert Vaughn, and was disappointed that he was neither the hero nor the villain, but kind of a speed bump for Steve McQueen's Bullitt. (And to this day I'm still puzzled by the plot -- I have to watch it again.) But I came away dazzled by the chase sequence, which I hadn't known was coming.
The cool thing about it is that it builds -- it's not just instant screaming tires and roaring engines. Bullitt plays cat and mouse with the two killers in the Charger at first, and the film really uses the San Francisco hills as setting; then the movie slams ahead into the chase. Dynamite stuff.