The overnight figure for "Asylum... " was 6.4m I think, so it's a drop of less 1million. The final figures might be a lot closer.
The ratings numbers are really besides the point as to whether or not newbies think the show is too complicated. River's storyline was complicated for a number of regular long term viewers, she was Moffat's pet character and only he wrote for her so her story took years to tell. And personally I could without the Rory/Amy soap opera. but then I never liked how Amy treated Rory and Rory IMO is the better of the two characters.