Just finally watched this. I got problems.
--The story was pretty thin. I believe budget has become a real issue, but still, it was too straightforward a story for a full-length Christmas special. It was really just a padded regular episode.
--I'm not sure what the point of linking it to The Lion, The Witch and the Wardrobe was--A Christmas Carol was an actual reinvention of the Dickens story, using the themes and ideas in clever ways, whereas this just borrowed some of the imagery from C. S. Lewis to no real purpose--but if they were going to do it, surely the TARDIS should have played the role of the wardrobe? I mean, he even said it was the wardrobe, but then it was the Christmas present that became the portal to the other world. That seemed like it was going to be the whole point of doing a TLTWATW pastiche.
--Why the hell was the Doctor doing all this anyway? I mean, I know it would be nice to believe he travels the universe, randomly sending kids on delightful adventures, but there's too many kids out there for even a Time Lord to personally play Santa to all of them, so presumably there was some other order of business and treating the kids was just a nice afterthought. So...what the hell was it? If it was just a "thank you" to the mom for helping them, he went about it in a pretty bizarre way, especially considering that he never actually met the kids.
--The biggest problem: if you're going to spend an hour trying to squeeze pathos from the story of a widow not being able to tell her kids their father died, don't have the father turn up alive and well at the end. That honestly makes me a little angry. Yes, it was framed in a rather clever way, but emotionally it was an enormous copout. It smacks of the often nonsensical "and then everything magically worked out for the best" endings of the Russell T. Davies era.