It's an utter pile of inaccurate shit.
For starters, rather than being a poor, man-of-the-people whose aim was to lead a raggle-taggle brigade of proud Scosts to freedom, William Wallace was actually a landed commoner with a good education, whose primary motive for fighting the Brits was protecting his own property. The film also shows Wallace bequeathing a son to the English Princess Isabella. In reality, however, not only did the two never meet, but Isabella didn't marry until 1308 - 3 years after Wallace's execution and her son wasn't born until 1312. And rather than the delicate humanist of the film, Isabella was a bloodthirsty harridan who later had her husband murdered, before launching her own invasion of Scotland.
Almost every detail of the battle is incorrect, with Robert the Bruce siding with the English King, dispite no historical records placing Bruce at the battle. Similarily fantastical are the scenes in which the Scottish nobles desert Wallace, and the Irish troops turn against the English.
To Cap it all, the blue face-paint which became the enduring image of the film had actually gone out of style with the Celts some thousand years earlier.
It's just another big budget Americanised heap of historically inaccurate gobshite, glorified to make things more interesting at the expense of much needed accuracy if you're going to touch a subject that still fires people up today