1968's "Bullitt" was selected in 2007 for preservation in the United States National Film Registry by the Library of Congress, as "culturally, historically, or aesthetically significant." I've been intending to watch it for years partly because of that, but also because it has possibly the best known car chase ever put on film.
The movie is essentially a police procedural, which is of course centred around Lieutenant Frank Bullitt. Steve McQueen plays the part so cool he's only slightly better than dead. He's put in charge of a federal witness for an ambitious politician (Robert Vaughn), but everybody's got their own agenda. The witness himself isn't particularly interested in playing it safe, and since he's stolen from a large crime organisation, people want to kill him.
The whole movie proceeds at a remarkably sedate pace by modern standards - we get to listen to coroner's laundry lists of a corpse's injuries on not one but two separate occasions, even though the list of injuries and technical jargon don't advance the plot except to show you what Bullitt is doing right now. I don't have a particular problem with this (many movies these days are too quickly paced), but it was interesting to notice how differently pacing was handled fifty years ago.
Many things are just handed to us at the beginning of the movie with a big fat "this is how it is," and at the end of the movie multiple things are left unresolved. I don't think there was an intent to make a sequel. The main case is solved and closed (by Bullitt, of course), but the whole movie feels a bit like an episode of something bigger. And the car chase was good, but no longer (in 2018) looks as outstanding as it apparently did then.