The film has difficulty rising above a rather depressing presentation, especially considering the supporting players, with the exception of some engaging moments featuring Sir Michael Gambon as the clever but somewhat underhanded Foreign Secretary Lord Edward Fox. It’s likely not improved by the fact that much of the story unfolds in a damp and somber 19th century England, but Ioan Gruffudd's portrayal of the abolitionist William Wilberforce feels underwhelming and weak. The same criticism applies to Benedict Cumberbatch’s depiction of Prime Minister William Pitt; generally, it felt like a straightforward recitation of historical events instead of an engaging drama that would inspire excitement about the contentious issues surrounding the parliamentary vote, which took nearly ten years to produce a significant result. There isn't much depth to the discussions presented, and while the film is open about its perspective, it fails to explore the reasoning behind the protracted timeline or the public’s seeming apathy toward these terrible events with thoughtful dialogue or well-developed characters. I felt that the movie too heavily depended on our natural discomfort with the topic rather than exploring the themes in a way that would be interesting and thought-provoking—and I struggled to stay engaged as it approached two hours. A thorough biographical account of this influential and committed individual, along with his allies and adversaries, would undoubtedly make for captivating viewing; unfortunately, this film doesn’t achieve that goal.

Source on TMDB