Regardless of whether the FF series is your sort of thing or not (and if not, I'm not sure we can ever truly be friends), you'd be hard pushed to deny that for a series now up to SEVEN films, they've kept a remarkable sense of continuity and an arguably increasing level of quality. Well, "production values" might be a more mass-acceptable term. What started as a fairly generic undercover cop/racing drama has ended up being a ridiculously over the top action series, while always keeping its tongue mostly in cheek.
Off the top of my head I can't think of another series with so many connected sequels which hasn't gone completely off the rails (for a given value of "off the rails"), except the Harry Potter films, which aren't quite sequels in the traditional sense, being based on existing books. The Police Academy films? Get out and don't come back. The Saw movies, maybe?
Casting has a huge amount to do with that (RIP Paul Walker, who will be sorely missed from the world, and any future films), but the movie-universe geek in me also really admires the timeline juggling they did to tie all the films together, or perhaps more specifically to make sure that the semi-unwanted stepchild of Tokyo Drift ended up fitting in with the others, in fact actually making it an important plot point for this one.
Anyway, in conclusion, these films are immense fun, and I have no problem turning my brain off and enjoying them mightily. Here's to Fast and Furious 20: 800hp zimmer frame.