John Simm was an excellent villain, but he simply wasn't at all believable as the Master to anyone familiar with the Classic series.
I wouldnt really agree with this at all. The character evolves and changes with each regeneratation just like the Doctor. He was very different to the ones who came before, but then the same can be said of Matt Smith when you compare him to the First or Sixth Doctors. I think the story was what made the character seem worse rather than the actual characterisation or portrayal. I am familiar with the classic series and I would say he was believable as the Master, he was just given a stupid story.