Whilst like his 1962 masterpiece, Lawrence Of Arabia, The Bridge On The River Kwai won for Lean both Best Director and Best Picture Oscars, his most ambitious film to that time is rather dated now in its unremitting indulgence in all things British (epitomized by the infernal tune "Colonel Bogey's March" whistled by the British soldiers at the film’s beginning) and an era-typical lack of realism.
The former is embodied by Alec Guinness (he had starred in Lean’s two Dickens adaptations, Great Expectations in 1946 and Oliver Twist in 1948) who won the Best Actor Oscar for portrayal of Colonel Nicholson, a stickler for Army protocol who manages to break his opposite number, Colonel Saito (Sessue Hayakawa), in a Japanese POW camp in Burma, through sheer force of will and goes on to build a better bridge for him than the poor Oriental fool could have ever managed himself.
The patriotic sentimentality is typical of late 1950s Hollywood productions (this was a UK-US co-production). Not only is there negligible recognition of the physical rigours one might expect from such an environment (in a scene when Nicholson inspects the progress on the first version of the bridge it seems more like a scout camp) but Lean strays into almost South Pacific-like hedonism with the character of Major Shears, played by William Holden, an addition to Pierre Boulle's original novel.
Lean tries to invest the film with moral conundra and a general condemnation of the madness of war (literally expressed at the film’s end by James Donald’s Major Clipton who has been critical all along of what he sees as Nicholson’s collaboration with the enemy), but the script is so burdened by its familiar typology of characters (Jack Hawkin’s Cambridge don is laid on with a trowel) and sanitized for mass consumption that it lacks significant dramatic bite. Whilst, as one would expect with Lean, technically the film is top notch(Jack Hildyard's Cinemascope cinematography also won an Oscar), today the film is largely for card-carrying members of the Returned Serviceman's League.
FYI: In 1984 the film’s screenplay was correctly credited to Michael Wilson and Carl Foreman who had been HUAC blacklisted at the time of it release and the Academy of Arts and Motion Pictures awarded them both belated Oscars.