I am currently watching the whole series (2005) again for the second time in a few months (I only got really into this show this summer during a tv rerun, though I had sporadically seen most of series 1-3 before that). Though now I am sort of pacing myself, as I am approaching the end of series 6 and hope to time it so that I am up to date for Christmas.
I thought Christopher Ecclestone did a good job and would have settled into it well, but I saw an interview with him and he was saying that the level of work involved in making it was too much for him and running him into the ground.
I think the most difficult aspect is that with Doctor Who, many characters are in many scenes, in different, widely spread locations (just walking into a building could be moving to a set hundreds of miles away), throughout an episode. They also do more running about and then there are things such as the CGI and green screen work.
Soaps are normally filmed pretty much in a single location and are far less demanding, once the plot-o-matic has written today's script.
We can see the actors at work in the Dr Who Confidential programmes that are shown shortly after each episode. It's quite fun to watch. What strikes me is that they often have to put up with primitive and sometimes very cold conditions.