What is so special about Doctor Who?

Have you ever asked yourself why Doctor Who is so special beside all the other TV shows out there?

I guess the first thing is that it has been there for such a long time now. In 2013 is the 50th anniversary of Doctor Who and which series can claim that it was more or less constantly on TV for 50 years. Doctor Who is now a part of the British culture and I guess everyone who grows up in the UK knows at least what Doctor Who is.
Another thing for me is, that I like the mixture of great stories and even greater characters. The success of the series always depends on who plays the Doctor and who are his companions. That's a big part of it all. They could have brilliant stories but if the actors are rubbish nobody would watch the series.
And then there is the concept of time travelling which opens you a lot of doors. You can let the stories happen in the past, present or future and nobody can tell you this can't be real. They even reboot the universe sometimes and undo things that happened before this way. Everything is possible with Doctor Who.
There are probably a lot more reasons out there why Doctor Who is so special and I guess everybody has their own set of reasons.
Fell free to share your reasons with me and leave a comment.