For most of its life, Doctor Who was shot in 24-minute episodes, usually with a series of cliffhanger endings that hooked the viewer for the following week's episode. The standard story was four episodes long. After more than 20 years, the producer Jonathan Nathan-Turner (perhaps due to pressure from the superiors at the BBC) experimented with changing the format to 48-minute episodes which were often self-contained stories (sometimes you'd have a 2-episode storyline). Despite the fact that the new format made for shorter, shallower stories and contributed to the demise of the show, the new series has followed this newer format. But for the new show, it has, in my opinion, worked better than it did for the 6th and 7th doctors. I still miss the faster yet longer storytelling of the original series, though. Which do you prefer?