I think Fast Five is pretty much a direct sequel to Fast and Furious. The series gets kind of confusing with the reboots, sequels with little relation to the main sequence, etc. Anyway, it starts where F&F ended, Diesel on the bus to Lompoc and his buddies coming to rescue him.
After they break him out, they hightail down to Rio to hide out in the favela. I kept expecting them to run into Ed Norton as Bruce Banner. They get into trouble with the local crime boss, Joaquim de Almeida, and decide to take him down. In the meantime, a big bad government agent comes searching for fugitive Diesel - yes, it's that other no-necked bullethead: Dwayne "The Rock" Johnson. This could get confusing, with 2 heavily muscled bald guys running around. But Johnson is so ridiculously bulked up that Diesel looks like a skinny kid next to him. So that's OK.
The movie plays out as a heist film, with Diesel bringing in his team from previous films, buying a replica of the safe he wants to crack, recreating the course they need to drive, etc. This seems like it should be in a different movie, possibly the Italian Job or Ocean's 11 remakes. In fact, I think I counted 11 in Diesel's team, but I might have been seeing double. And there is a garbage truck playing the same role as in the original Ocean's 11.
It all builds up to a fun and literally unbelievable climax. -SPOILER- two cars could NOT outrace all the cops in Rio is they were dragging a 10-ton safe. Could they have at least put a creeper under it?
Never mind, it's all in fun. Some (Ms. Spenser, for ex) might prefer more car chases, but there's plenty of action, and not too much romance. One of the hookups was between Ms. Spenser's heart-throb Sung Kang and Gad Galot. I have to agree with the Ms. - she's cute, but too skinny. She wouldn't get a second look in Rio.
Make sure to watch to the end - set up for sequel.