Doctor Who, Stargate, and Star trek all have the mobile set going for them. They can just pop in to a new setting each episode. I think Dr. Who is so good now because they have had 40 years to get it right. They have a huge selection of excellent recurring villains, and they've found the wacky, brilliant, mysterious Doctor and strong female sidekick archetypes that really appeal to the audience. It's hard to beat.