the opera is much more gritty than the film. britten's music is never sentimental and there is a kind of starkness about the opera. He really meant it to be his swansong - as indeed it was. Tadzio is a dancer in the opera - a stylistic representation of his beauty which would probably work well in the theatre but I saw it on tv and it didnt quite work. (opera on tv is always a challenge)
Whereas Visconti concentrates on the decadence of Venice and keeps everything ultra-beautiful, Britten concentrates more on the heat and pain of it all somehow.