The plot concerns the officers and crew of HMS Surprise, one of His Majesty's navy's smaller and older frigates, which has been assigned the vital task of intercepting a French privateer bent on disrupting British commerce in the South Seas. (In the novel, the enemy vessel was an American, but it was probably judged correctly that, at least for the US market, having a US opponent was not a good idea.) Initially, the crew of Captain "Lucky Jack" Aubrey is confident of victory, until the "Acheron" proves to be an opponent that is newer, faster, tougher, and more heavily armed than the Surprise, and captained by an annoyingly craft skipper, to boot. Interestingly, the design of the Acheron is based on the USS Constitution, which was indeed the "battle cruiser" of its day.
Things begin to get tense when Aubrey, Ahab-like, persists in chasing the "phantom ship" far beyond his area of operations even after the Surprise is nearly destroyed in their first encounter. The scenes of sailing, ship-handling, and naval combat are the best I have ever seen, as are the everyday scenes of shipboard life, dirty and crowded as it is. Oscar winner Russell Crowe does a very good job as the big, bluff, blonde Aubrey: not an intellectual, but a masterful sailor and fearless fighter, and many of the characters we have come to know in the novels, such as Barrett Bonden, Aubrey's faithful steersman (played by Billy "Peregrine Took" Boyd) and Preserved Killick, the Captain's irascible steward are easily recognizable.
I predict that the casting of Crowe's "A Beautiful Mind" co-star Paul Bettany as ship's doctor Stephen Maturin will prove most controversial among O'Brian fans, with reason. It isn't that Bettany isn't a good actor, and he works well with Crowe. The character he creates is a very complex, sensitive man, courageous, but not military, fixated on his sciences to the point he is frustrated with naval necessities. While all these are part of the literary Maturin, the man in the books is small, dark, and wiry, a deadly duelist and a sure-handed surgeon, but a total "lubber" when it comes to the sea. In the film, we never even see the notably tall Bettany so much as hit his head on the low below-decks overheads. O'Brian's Maturin is half-Irish (and took part in one of the many failed rebellions) and half-Catalan, but the only way we would know Bettany's character is anything but an "Englishman" is because he tells us he is Irish. (For that matter, Crowe's Aubrey doesn't have a discernable British accent either, although the kind of mid-Atlantic in use by many Australian actors blends in with the natural variety of voices found in the crew so as to not be jarring.)
Highly recommended. The violence is intense, but realistic, and should not deter any but the most sensitive viewers.