This film received rave reviews in the New Yorker, Wall Street Journal and our local newspaper.  British accents, the background noise from rooms full of people, multiple conversations, whispered conversations and comments made by actors walking away from the camera.....all contributed to incomprehensible dialog..  Much later we rented this on DVD and watched it with close caption subtitles. If you have any hearing impairment at all, I recommend this approach.  

The film was excellent.  It is an English mystery classic in the grand style of Agatha Christie, but as one critic mentioned, well beyond her work in both subtlety and in the shear number of characters.  Speaking of characters, Maggie Smith is always good and in this she was wonderful as the countess.  Alan Bates (King of Hearts) made a great butler.  Derek Jacobi is a stand out as the 'great man's' valet.  And the list goes on.  The cast is incredible.  Some of that famous British humor is introduced when the bumbling inspector arrives on the scene.