JFK, as if you didn't already know, concerns the story of real-life Louisana District Attorney Jim Garrison and his (ultimately unsuccessful) prosecution of Clay Shaw for conspiring in the murder of President John F. Kennedy.
Through an audacious technique of sound and image editing, combining different film stocks and overlapping dialogue, JFK is a powerful piece of cinema that deserves a place in everyone's collection. It is to director Oliver Stone's credit that he keeps the viewer continually engaged with the film through it's three hours and seventeen minutes running length.
The film is not only a significant technical achievement but supremely enjoyable on a purely cinematic level. The cast is uniformly excellent - a special nod of the head to Gary Oldman as Lee Harvey Oswald - and Robert Richardson's cinematography is, as always, gorgeous.
Due to the inflammatory subject matter (a U.S. covert action program designed to assassinate foreign leaders gets blown-back and turned on President Kennedy), this film and those associated with it have often come in for a lot of highly charged invective. Therefore, some background reading is highly recommended; if you only read one book on the Kennedy assassination, make it Oxford historian Anthony Summers' "Kennedy Conspiracy" for an in-depth and reasoned analysis.
In short, this is Oliver Stone's "J'accuse!" -not only one of the best films ever made but also one of the most important.