Yes, I'm a Banksy tragic - but this goes beyond that. It's simply an excellent movie that explores the issues of reality and validity and originality in art. And does it in a side-splittingly funny way that both intrigues and confounds. I came out of it the first time saying "I don't think I believe anything I just saw!" but the second time around I think I get the 'truth' in it. Or at least the point that it's making.
Both times I appreciated that it wasn't necessary to know whether it's a documentary or a mockumentary (or, as a brilliant friend coined, a 'prankumentary'), it works as a film without that certainty. And I think is a much more long-lasting film in the way it has been made - a more straightforward exploration of street art and graffiti artists would have only limited appeal to the general public. While I'm sure this won't be hugely popular with the urban art unaware (not as much as it should be..) I think it'll become one of those cult films screened many times over the years.
It's possibly just my love of irony and ambiguity that made it resonate so much with me - your mileage may vary. But I really can't recommend it enough. Even if you have no interest in street art, trust me - this is one excellent and funny film.
Whether Thierry Guetta exists as a real person or a construct he is hilarious to watch, and the last word should go to Banksy:
There's no one like Thierry, even though his art looks like everyone else's.