Though I did start the first one with the original ITV1 promo...just to set the mood.  Then it's on to footage accumulated over the past year, with interviews of cast members and a tour of Highclere Castle, the estate where Downton is filmed.
If you want to grab a cuppa and settle in for a bit, I'd encourage you to watch the video "Downton Abbey Season 2: A special Q & A" this interview lasts about 45 minutes and was filmed just a couple months ago in New York.  It's fascinating to see and hear all the actors speaking about the Downton effect on their lives.  Enjoy the videos I've picked out for you!