Matt Smith is, of course, a great Doctor. Unfortunately for him, he has to follow David Tennant. As old-school Doctor Who fans remember the likes of Tom Baker, Peter Davison and the others, I and likely a great majority of new fans will remember David Tennant, with Chris Eccleston coming right behind him.
Matt Smith, eh... There's something about his face that doesn't quite sit well. The Doctor needs to be able to display an incredibly wide variety of emotions with nothing more than their face muscles. Chris Eccleston did that very well, David Tennant took it to a whole new level, and Matt Smith, well, not quite so much. Both David and Chris could do "furious, righteous determination" very well, and that's something that I rather like in The Doctor, is his ability to let the villain know how horribly screwed they are. Matt Smith, bless his heart, doesn't quite have that ability.