Well, how can I not chip in here 
Having said that though, I love absolutely everything about it so much that it's almost hard for me to talk coherently about it.
It's an amazing piece of work that, first, could only be a film. It's a sort of collage documentary/rumination on just about the biggest ideas you can image: the nature of art, truth, storytelling, all kinds of stuff. But at the same time it's a lot of fun. The story of the art forger Elmyr de Hory and his biographer Clifford Irving is just a really interesting story in and of itself, and de Hory is a great character. But then when Irving himself becomes the perpetrator of a famous biographical forgery, the whole narrative takes on a kind of hall of mirrors quality which Welles is then reflecting (pun somewhat intended) in the way he puts the film together.
And as part of the whole theme of forgery, truth and whatnot, I just love the way that Welles is kind of mischievously messing with you during the film. So at the beginning of the film he sets up the theme of movies being like magic tricks. That's of course a total cliche and he knows it (though no less true for that). But then parts of the way the film is put together make you think that you're getting a look "behind the curtain". There are scenes that appear to take place in an editing suite, and in other scenes Welles speaks (and edits the film) as if he's in a particular location seeing something when he's manifestly not. But then, that's nothing more than what he wants you to see, so the peek behind the curtain is just another instance of misdirection. The whole thing works though because Welles possesses such a casual, off-hand mastery of the art of storytelling, and the storytelling aspects of film particularly.
[For people who might know him, it's exactly like what Derren Brown, the British illusionist/mentalist/magician/whatever sometimes does in his shows. (And for anybody who doesn't know about him, run as fast as you can to see anything he's ever done.) He'll occasionally suggest, more obliquely or less obliquely, that he's achieving his effects in a certain way (never by psychic powers, just seemingly plausible-sounding psychological or statistical phenomena), but again it's just more misdirection.]
The editing is justifiably famous of course, and it's great on both a global and local level. So the film itself is, as I say, kind of a collage of part of documentary film about Elmyr de Hory which had already been shot, plus new footage by Welles (with the documentary director as his cinematographer), with then some other setups involving Oja Kordar. The fact that the whole thing isn't a complete train wreck is a minor miracle. And then on a local level, the editing of individual scenes is really well-done, both in terms of the way things are juxtaposed and the relation to the narration.
And, man, the narration. I could listen to Orson Welles reciting the proverbial phone book. If you get the chance somehow, do see "The Orson Welles Sketchbook", a series of shorts that he did in the 50's for the BBC where he reminisces about various topics in his life and does sketches to illustrate them. Just listening to him speak is amazing.
Anyway, if you're willing to be drawn into this kind of always-joking-and-always-serious free-form world/essay that Welles is creating, I think F for Fake is just absolutely fabulous. It's the work of a complete master and a complete genius just doing totally his own thing (not to, like, oversell it or anything).
) It's not like there's any shortage of "war is hell and sucks, and battles are confusing" moments later on. 