I think it was difficult for the producers of "Dr Who" to choose a new doctor.
They had already said they didn't want a mature Doctor,which rules out Robert Carlyle and Richard Armitage (Matt Smith is 26)they also wanted a good actor,but not someone associated soley with another series,which rules out the anyone from Eastenders or Casualty.
I think it it just this amount of "unknowness" that led them to choose Matt Smith.
He has mainly been a stage actor up till now.
I think a fresh unknown face is just what the Doctor needs,and I have been watching Dr Who since 1963!