I watched Fast and Furious the other day, and was pretty impressed. The whole thing came across as the sequel everyone wanted, instead of what they ended up getting in parts 2 and 3.
Last night though, I watched Fast 5 in the theater, and was blown away. It's full of nods to the previous movies, but surpasses all the movies that came before it in the franchise by a long shot. It embraces the kind of over the top machismo-oozing that put me in mind of the first Predator movie. It also knows when not to take itself too seriously, and has a good chunk of laughs/ridiculous moments. I'd rank it up there as one of the best American-action movies I've ever seen.
Highly reccomended.
Also: The Rock is ridiculously badass, and delivers some equally ridiculous lines. Hoolarious.