Catherine Tate in Doctor Who

With the forth series almost upon us (next week in fact), it might be worth commenting upon this.
There has (apparently) been a vocal outcry for the choice of Catherine Tate's character of Donna replacing the character of Martha within the series.
Russel T. Davies is obviously aware of this because he has spoken out against the criticisms, saying that it is absolutely not true that Catherine shouted her way through the Christmas 2006 special.

Well, I hate to disagree Russell, but that is exactly how I would describe her portrayal in the special. Unfortunately, the story was overall weak and disappointing, not just because of the "shouty" Donna, but also because the villain of the piece (the ancient and feared Empress of the Racnoss), basically spent all her time hissing and snarling at her enemies and didn't give the impression of being an ancient technologically advanced and intelligent being. The "Star" spaceship shooting lightning was also a bit poor.

So ... what of the news that she will be appearing more in the series?
Well ... I thought it was interesting that some of the discussions focused on the fact that Billie Piper had been an unpopular choice when she was first cast, so it was unfair to pick on Catherine Tate.
There are however, one or two critical differences.
- Billie Piper had not acted much and what she had done (Canterbury Tales) had been considered very good.
- Catherine Tate is a capable actress, but has actually appeared in the series as this character already, so therefore judging her performance in the series is a lot more straightforward.

Having said that, my complaint is not with Catherine Tate particularly, it is with the character of Donna. I am hoping that the "shouty" Donna will be toned down a bit (or a lot) for the new series and that the character will therefore be more reasonable and sympathetic.
Still would have preferred Carey Mulligan though (Sally Sparrow from "Blink").