Extremely underwhelming. It felt very self-fulfilling almost like a 90 minute advertisement more than anything else. Also, in keeping with GT's development process, it definitely came off like Kaz and PD work in a total vacuum and don't acknowledge that there indeed are others out there that do the same things they do. It's not as if they're the only ones doing these things, but they sure act like it. The segment about how they laser scan the tracks, for example. Pretty much every racing game out there does the same stuff as you're doing, Kaz. Sorry to break it to you.
As another user pointed out, it also seemed very awkward and all over the place like they didn't know if they were making a documentary about how GT was created, Kaz and his life, how digital entities such as GT have been affecting the real world, and so on. Not exactly a well thought out or well constructed documentary from that standpoint. Also some of the camera work, especially during interview segments with Kaz, was unbelievably annoying. Zoom in, focus, zoom out, zoom back in, focus, zoom in more, zoom out, zoom out more, focus, shake the camera, zoom in, zoom out, focus....etc etc etc. It was overdone and just plain annoying. Also one of the subtitles had a misspelling. That pretty much shows the level of care taken here to me.
So yeah, overall I was very underwhelmed by 'Kaz'. It just wasn't very interesting, well thought out, well constructed, the interviews were awkward in places including Lucas Ordonez flat out saying "I don't know what to say" while motioning for them to cut, for instance. He's not 'overwhelmed' and in 'awe' and 'lost for words', he just ran out of ways to stand there and continually kiss Kaz' ass for the cameras. What else did they want him to say, ya know? Surprised they didn't cut that. Anyway, I'd give it a 1/5 at best. It was what I expected of it from the trailers, though. Basically a 90 minute ad for Kaz and GT.