While I'm still watching the series myself (beginning of season 6) I decided to make my mom watch Doctor Who, as I knew she'd love it. About 10 minutes into the first episode and she told me she was already addicted. We blew through half a season today.
Watching some of my favourite moments with her, and watching her (attempting to) figure things out has been a lot of fun, and I know as the story gets more complex, will be even greater.
What series have you introduced people to? Did you have fun with their reactions?