What a weird little movie!
It's a cult classic, of course, and one I've heard people rave about for eight years now, but I'd never made time to see it.
Now that I have, I can better understand the two camps: (1) The die-hard fans who LOVE it, and (2) The befuddled who don't.
I'd say I fall somewhere in between: I understand and respect its single-camera set-up, its 'documentary'-like vibe, and the majority of its scenes involving 'real people' (non-actors) being approached by and reacting naturally to Scarlett Johansson. All that is lovely, fascinating, and pitch-perfect.
As for the rest, and the film's meaning, don't expect to be entertained in any proactive way so much as to be voyeuristic as a strange woman in a strange land navigates and hunts.
Think Predator, but performed a cappella, zero electricity, and sans audience, and you'll have a general sense for what is—and what is not—about to happen.
I do recommend it, but only if you like noir, silent films, and sci-fi fantasy... because somehow, on some level that's hard to explain, it's got the essence of all three without quite being any of them.
Like improv, but more somehow.