Bullitt -- A Classic
By today's standards this may be a slog. The difference is that Bullit is realistic compared to modern-day equivalents such as let's say the "Bourne" series). The premise here is straight-forward, easy to follow, with few pyrotechnics.
McQueen is great because he has almost nothing to say, but when he does, it holds an impact. He doesn't come off as half-super-hero/half slick cop, but as a persevering, smart and yet very ordinary detective.
The car scene is famous because it is the first of it's kind -- and it too looks absolutely real -- as opposed to the clearly impossible car chases in modern films. The cars speeding over the bumps of the streets of SF are getting smashed up, losing hub caps, smashing their under-carriage. They aren't driving on sidewalks, plowing through kiosks or even indoor malls. People (civilians or bad guys) are not landing on the hood and looking into the windshield).
The trip may seem slow when compared to the hyper-kinetic action scenes of modern movies, but you don't have to give up as much to the realm of implausibility. Also, bear in mind that "Bullit" was a first. It was the film from which everything else in the genre would emerge.
The on-foot leg-chase through the airport landing strip could have been spliced right out of this film into Michael Mann's "Heat." The adversarial relationship between McQueen and Robert Vaughn (as a DA) has been done a hundred times over because of this film.
The film is indeed a classic, but it's important for newer viewers to know why. If you think this is a snooze-fest, have a cup of coffee, and stick with it. If nothing else, you'll be absorbing a bit of film history.