What do you think about the trend towards extended story arcs in movies and television?

Do you enjoy a movie or television episode more if the plot is completely self contained or do you find yourself preferring shows that build a plot line without resolution until the end of a season?

I have seen this trend develop across television, and with the Avengers coming out soon, it appears, at least to me, to be spreading across into movies.

Do you enjoy this trend? Are we losing the ability to start watching a show in the middle and gain any enjoyment from it?