Kopel carefully documents 59 instances of deceitfulness, if not outright lying, by the filmmaker. Kopel's conclusion is that the first part of the film (about Bush, Saudi Arabia, and Afghanistan) is "so permeated with lies that most of the scenes amount to lies". The second part, about the USA PATRIOT Act, arguably presents useful information. (For the record, I've never been comfortable with the PATRIOT Act's clear infringements on civil liberties.) Some parts of the third portion, on Iraq, are outright falsehoods; others, while not blatant lies, are so extremely one-sided that the overall picture of the Iraq War is false.
Moore certainly has the right to make whatever movie he wishes, especially if he can convince gullible leftists to give him lots of money to be preached at and lied to. (A curious thing for someone who hates capitalism to do, but that's a separate rant.) I certainly wouldn't dignify the work as documentary, however, as it's not truth, but propaganda. It's no more documentary than the films Stalin had the great director Sergei Eisenstein make before WWII.