Seriously, it is the job of the reviewer to point out the horrific and the extraordinary.
The most fun is pointing out the extraordinary.
Imagine that:
1. You are possibly the greatest living TV writer. The jury will not be in of course until you pass off this mortal shell, but the evidence at hand is substantial.
2. The year is 2010.
3. Among your many past accomplishments is that you have taken a children's show from the BBC archives and given it a worldwide stature that exceeds both Star Trek and Star Wars. That is cool. Like bowties are cool.
4. And that is merely your day job. At X-Mas, you get to have extra fun by writing "specials" that fans around the world await.
5. Again, the year is 2010. You decide to go for broke and write something which will not only be as good as Dickens but, hey, why not try to improve on the original?
6. Your logic is something like this. Even the BBC executives won't see how ambitious your work is, because the "Christmas Carol" theme has been done to death in movies and TV, and no one ever has come close to the original. So you proceed under cover of stealth. And cynicism.
7. And you nail it. A perfect supporting cast that includes no less than Michael Gambon and Katherine Jenkins.
8. And writing to die for. Writing beyond belief. There is a scene where Gambon, realizing that the Doc is playing him, challenges the doctor to "go ahead, show me the future" and the Doc replies, "That is what I am doing" ... pan camera to show that the younger Gambon is already in frame and the dialog with the older one was for the benefit if the younger. So, in effect, the future has already been shown.
9. And THAT is just a sample of the writing. The fact that this comes at the end of a Amy/Rory arc -- now considered (2014) to be the best arc in the series EVER -- is merely irony. Piling greatness on greatness.
10. Memo to IMDb staff (as if they are EVER going to reply, even if this is being written at X-Mas) -- we need a higher rating than "10."
Just for special occasions. Like this one.