I know I'm a bit behind the times, and it's been out a while, but it wasn't exactly a blockbuster release, y'know?
I went in thinking it would be an 'anti gun' film. I didn't come out feeling that it was 'anti gun' - the comparison with Canada put paid to that notion.
The main message seemed to be the climate of unjustified fear which the US (and to an increasing level the UK) is living in - though the UK hasn't a patch on the US. This climate stoked by the media's focus on disaster - it being much easier to report quick effects rather than complex causes.
The thing which really hit home was the city in Canada, across the bridge from Detroit, where Moore walks up to random front doors and finds that, yes, they really don't lock their doors in Canada. (It doesn't indicate how many were locked, but it was amazing to me that any were unlocked)
If you go to the website, two clips particularly worth watching are 'A brief history of America' and 'Michael goes to the Bank'.
This is a film to watch, it's a little long and I can see that some people may not agree with everything here - but there are certainly elements to make people think.