Actually a 6, arguably a 7 for comedic value...

Rating: 1/10 (2 April 2015)

But I'm giving it a 1, because of all the Walker Dead fans who upvoted. Will adjust after it's between that range. As for the franchise, it's flogging a dead horse. I mean they had started with drag racing, went on to drifting... this installment literally had cars flying EVERYWHERE.
Smashing, jumping, flying, floating, cloning (Maserati), mating (Jeep?) cars... And The ROCK gets a car (sort of) too! Plot is par for the course, slightly dumbed down for the audience of today. (E.g. Kurt Russell's role and the MacGuffin tech nonsense)
Overall, enjoyable show especially near the end where the action crosses into the ridiculous territory. Next installment, do F1 please.