Honestly, I didn't think it was the best Christmas special ever. There was just nothing really special about it, IMO. Also, the beginning with the Doctor surviving for such a long period of time in the vacuum of space really strained my suspension of disbelief more than usual with a Doctor Who episode. Granted there could've been an air corridor there, but it just feels way too convenient. The end with the Ponds was probably the highlight of the entire episode. Some goods lines in there too though. But all in all, a fairly average episode.
Thinking about it, this is probably how I'd rank all the Christmas specials together:
A Christmas Carol (2010)
Voyage of the Damned (2007)
The Christmas Invasion (2005)
The Doctor, the Widow and the Wardrobe (2011)
The Next Doctor (2008)
The End of Time (2009)
The Runaway Bride (2006)