Whereas the first three films focus primarily on street races and the people with a lack of screen presence that love them, Fast & Furious, along with Fast Five and Fast & Furious 6, took all the vroom vrooms and implemented them into what would become, basically, heist films, a far more exciting route than having characters frown at each other in between screeching tires for 100 minutes.
Now they drink beer and seizure-smirk at each other.
Secondly, they created a stronger overarching theme, primarily based around the importance of Vin Diesel's favorite word in the series ("Family," Diesel said thoughtfully, doing something with his mouth that sort of looked like smiling). And, to top it off, they added Dwayne "Don't Call Me 'The Rock' OK Maybe Just Once" Johnson, a human cartoon character who provides the kind of macho, self-aware performance that really anchors the tone of the series.
And single-handedly saved the baby oil industry.
The films are filled with more ludicrous situations than ever, but rather than the overly serious manner of the early efforts, the recent installments seem to be approached with a sincere embrace of all the booming, ridiculous action. The cast and crew are cognizant of the insanity of parachuting cars out of a plane in order to chase a bus, and they're prepared to make it the most entertaining, well-constructed scene of parachuting cars out of a plane to chase a bus that you've ever seen. I predict that Furious 7 will be Ludacris' first foray into the Criterion Collection.