Although its been shown to have been largely fictionalized, the gist of the story is accurate. Oldman gives an incredible performance, and not as some old bellowing windbag either.
After seeing this, one might recommend reading churchill's own 6 volume set on the subject, but to save time, the first volume, The Gathering Storm, may provide one with some historical pretext for this monumental event in western history-Churchill standing up to a madman, and this saving not just britain, but all good men everywhere.
Oldman, you da man!