A lot of people think it's a gas to pick on Michelle Rodriguez, but I'm not really concerned with her acting abilities -- she fits in with the franchise well enough. It's the motivations of her character, Letty, that are more concerning and ultimately baffling.
If you remember, Fast 6 reveals that Letty did not actually die in Fast 4, but instead got hit with a nasty bout of Car Racing Movie Amnesia. The bad guy of F6, Owen Shaw, picks her up at a hospital and decides to use her skills to his own end. Shaw is a nutball, so it's not really surprising that he took in a former enemy; what's really troubling is that Letty went along with him instead of like, finding out who she actually was.
It becomes clear that she's with Shaw's shady crew more or less of her own volition, almost as if losing her memory made her lose her moral compass. Even when Shaw goes nuts with the tank and starts crushing SUVs for fun, Letty is only mildly miffed.
She whines a little, sure, but when Shaw demands that she go fix something on the outside of the tank currently speeding down the wrong way of the highway and killing innocent people, Letty has no problem with that. She's still completely under Shaw's thumb until the moment Dom Supermans her out of the air.
After that, Letty is magically in cahoots with the good guys again, despite not having her memories back. She seems to just roll with whoever's around and act like it was her idea all along. Which makes it all the more infuriating when Letty says this:
Dude. Letty. Ever since you got that bump on the head, you have been doing nothing but what other people tell you to do.
Maybe the saddest part of this whole ordeal? Poor Elena gets shafted. She hooked up with Dom when he thought Letty was gone, but she gets dumped the moment his old flame comes snarling back to life. And she's somehow totally okay with it?
She leaves Dom willingly, and without a fight, just accepting that this amnesiac has ruined her life. I hope she knows that her immaculate cheekbones were too good for him anyway.
The last action scene in Fast 6 is bonkers in a great way, but it also stretches plausibility so hard that its arm snaps and this weird goo starts coming out and you have to return the Stretch Armstrong to the store. The whole thing revolves around Shaw trying to make a getaway while the gang chases his plane on a runway. In something like Goldeneye, a land-based plane chase lasts about 90 seconds. But here? They're on the runway going full speed for 13 minutes. 13 minutes going as fast as a plane just before landing or takeoff.
The heroes infiltrate the plane in time and stop the escape, but it still takes 13 minutes to do so. In that time you could cook a frozen chicken pot pie, take it out of the microwave and still have plenty of time for regret to sink in. They don't even run into the pesky "out of runway" trope. When the plane explodes and Dom's car comes roaring out of the nose (man these movies are so awesome), all of the other drivers manage to skid to a stop with plenty of room to spare.
A few outlets have tried to determine the exact length of the runway by factoring in the speed and duration of the chase; most put it at around 28 miles. For reference, the longest paved runway on the actual planet Earth goes for just over three miles. So that makes the universe of Fast and Furious about nine times more ridiculous as the real world. Sounds about right.