Confession: I had not watched a Fast and Furious movie until a couple weeks ago. I was under the impression that they were a steaming pile of soulless action garbage, like the Transformer series.
Subconfession: I have not watched a Transformers movie either, rendering the previous sentence completely irrelevant.

Anyway, I fired up the first movie some time ago, then proceeded to watch the other six. I was positively surprised to find warm, goofy action movies with clever casting. Spoilery impressions of each movie below:

The Fast and The Furious: I liked the friends and family focus of the movie. I also appreciated that, despite the premise, the main characters being suspicious of each other did not dictate the course and tone of the whole movie. The film was surprisingly "down to earth". For example, I loved that one of the most emotional scenes was a side character losing his father's car in a race.
2 Fast 2 Furious: I have practically no recollection about the plot of the movie. Something about drugs? Also, where is Vin Diesel? Totally forgettable.
Fast & Furious: The plot is still not very memorable, but at least Vin Diesel is back.
Fast 5: Oh my god, this is one of the best heist movies I have ever seen. Like Ocean's Eleven with cars, where the director doesn't pretend that George Clooney, Brad Pitt, and Matt Damon are not the same character. Amazing cast, great tone, whacky action. And those ridiculous Vin Diesel and The Rock moments... ugh. I hope they keep it up!
Fast & Furious 6: Nope, they've done fucked up. The cast and action is still great, but this movie has borrowed too many elements that I absolutely despise from modern action movies: A deeply sadistic antagonist; a previously empowered female character being downgraded to a target, victim, and motivation for the male leads; the killing of side characters just to give other characters a darker backstory; and the "just kidding, world is still shit" ending. I hope Furious 7 corrects the course. Meanwhile, it is time for...
The Fast and The Furious: Tokyo Drift: A fun movie. Unfortunately, the casting did nothing for me with the notable exception of Sung Kang. I was glad that Tokyo Drift was not as dark as Fast & Furious 6 despite the shared ending. However, this movie makes me even more angry about Fast & Furious 6, as it shows that Gal Gadot's character was killed off (without a funeral or anything, by the way) just because Sung Kang's character didn't have a woman in Tokyo Drift, and that Sung Kang's death was clearly not caused by a sadistic Jason Statham.
Furious 7: Oh wow... They dropped the ball even more spectacularly in terms of tone as compared to Fast & Furious 6. Jason Statham plays a good baddie, but it just doesn't fit this series (or more precisely, my ideal for this series). He is sadistic to the point of being ridiculous: In the first scene he visits his comatose brother, swears revenge, threatens to kill the hospital staff if anything happens to his brother, and then pretty much blows up the hospital. What the fuck? Also, yes, eye in the sky surveillance, and attack helicopters and drones is just what this goofy car movie needs...

And 8: I have zero reasons to go see this. The relationship between Vin Diesel and Paul Walker was one of the best parts of the whole series, and Walker's goofy smile whenever he realized he was surrounded by friends was genuinely uplifting. With Walker dead, and some of the more interesting side characters gone, and with the series seemingly committed to ramping up the tension, darkness, and brutality, I see no way for the next movie being interesting to me.

Anyway, I don't regret watching the whole series. It was worth it for The Fast and The Furious and Fast Five alone.