I've seen all of the previous FAST & FURIOUS (FF) movies--or at least I thought I had--somewhere I lost count because I can only recollect 4, but I'll leave that for some other time.
I'll say up front that while these movies are silly, I really like them--a couple more than others, but overall I find them entertaining, well-made, and perhaps most of all, they provide a "feel" that I find comforting, familiar (I grew up in a car culture), fun, and exciting. While some movies have great visuals (which include FX), others have great stories, and other have this third characteristic which are known as feel or ambiance.
It could be argued that the two former characteristics produce the third, there are plenty of movies that have neither exceptional visuals or stories, but produces a feel that separates it from other movies. While something like feel is absolutely subjective, there's no denying it exists. (Think of movies that you like that are just as welcome being on while you watch intently or provide a sense of comfort just being on in the background and you'll understand what I'm talking about.)
FAST & FURIOUS 6 (FF6) is a prequel to FAST & FURIOUS: TOKYO DRIFT (my favorite of the series) and it brings our favorite characters from the other movies together. While there are some really implausible things in the movie (like the world's longest runway!), I don't find myself caring too much because it's a fun movie that has a lot of heart. I think one of the major aspects of the series that makes it appealing to me is the theme of family doesn't have to be blood related. It hits home for the road rat culture.
It's not a movie (or series) for everyone, and while I'd place this one as a strong #3 in the series, I really liked FF6. I will watch it again when I re-watch the whole series (probably in timeline order), but I don't think I'd watch it by itself as I had with other installments.
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As a side note, while it's very sad that we lost one of the "main" (perhaps "original" is a more accurate description) actors from the FF series, PAUL WALKER, he didn't appear in every movie in the series, so I suspect we'll see FF movies for years to come. If there's a silver lining or purpose to this tragedy it might be that it drives home (pardon the pun) that what goes on in movies has real-life consequences.