The contemporaneity which made Sunday Bloody Sunday such a success in its day is the same thing which dates it. Like so many films of the time, it takes on the values of the new, permissive society, specifically a commendably candid treatment of middle-class homosexuality and the period's subscription to 'open' sexual relationships.
Bob (Murray Head) is having simultaneous affairs with Alex (Glenda Jackson) and Daniel (Peter Finch), both of who resent the other and yearn for monogamy. This is depicted as a generational conflict, something which gives Schlesinger the opportunity to contrast the groovy and not-so-groovy lifestyle of the Now Generation with that of the conservative Establishment (a family of free-thinking liberals provides the middle ground).
Whilst the performances by Jackson and Finch are convincing and the script by Penny Gilliat is intelligently 'mature', everyone is so damn reasonable about their angst that dramatically the film fails to arouse much interest whilst Schlesinger's commitment to giving a portrait of the times burdens it with an excess of information. Watch out for a very young Daniel Day-Lewis, briefly seen as a car-scratching vandal.