I didn't now anything about Catfish going in other than what I learned by looking at an insert in a NetFlix mailing. The insert had a bunch of rave blurbs (of course, even a bad movie can round up a passel of rave blurbs) and a warning "Don't let anyone tell you what it's about."
In the spirit of the distributor's wish, I will write no review, because to write a review would be to spoil the experience. However, I will say this: Catfish is a documentary. Not a dry, after-the-fact sit-down docu, but a let's turn on the cameras and see what happens documentary.
If the surprising and unexpected is what you like, Catfish is worth seeking out.