The only complaint I have heard yet about the film is that it reportedly portrays Wilberforce as somewhat of a secular humanist and tends to downplay the deep religious motivation he had for abolishing the British slave trade. I haven't seen the film, so I cannot comment, but if it is true then it is one more sad effort to re-write our noble history.
http://catholiceducation.org/articles/arts/al0306.htm

Aye,
Matt