If you don't have plans to see this movie, you can check the spoilers here and then come back.
Half hour or so removed from finishing this and still somewhat wrapping my head around what I thought of it, including to what degree I liked it, so this may be a bit less focused than my typical review (if that's possible). A huge part of my viewing experience mirrors most other people, I wager: I was devoting a great deal of effort to trying to figure out if this was a legitimate documentary or not. At first I did not, then started doubting as it went; according to what I looked up after, the creators claim it's legit, though many folks are dubious. The main reason I thought it was fake was what I chalked up as poor acting from Nev Schulman, but apparently he wasn't acting, so I'm not quite sure how to evaluate it then. Indeed it's hard to really quantify the quality of most aspects of this piece given that it (supposedly) is real; even other documentaries I've seen set out to tackle a subject and put a spin on it, whereas this was a case of two guys apparently having the insight and or lucking out in chronicling a fairly interesting story as it developed and sticking around as it became something much more. The stuff I can judge--the editing, the filming, the visual cues--were all well done, particularly the way they incorporated actual Facebook graphics into cuts. Iit was a job well done and can't find any glaring technical faults. The "story" was extremely engaging and they did a good job walking the line between uncomfortable and touching. However, it didn't strike me as revolutionary and I don't have any strong desire to watch it again despite having probably missed a lot while trying to play detective. Going with my gut, I'll rate this above average but wouldn't go any farther than that.