Derivative as most of Moffat's work for Series 8 and he doesn't do a damn thing to hide his sources. Still, it's hard to be a Grinch with Nick Frost as Santa Claus and the script does a fair job of balancing horror and comedy while Capaldi and Coleman make everything work through sheer charisma.
Clara Oswald is woken from a long winter's nap to find Santa Claus and two argumentative elves on her rooftop. The Doctor arrives not long after to tell her that humanity is under attack. Telepathic alien parasites that force their hosts to dream of a happy life as the vitality is sucked out of them have been awakened and it is up to The Doctor and Clara to save a team of scientists that are trapped at the North Pole.
The problem is that it's all but impossible to tell that you are dreaming once you are caught and harder still to escape the Dream Crab's influence... even with obvious clues such as the presence of Santa Claus to warn you that things aren't real. So why does Santa keep showing up trying to save everyone? And just how deep does the dream go?
THE GOOD PARTS
* For all its flaws, the script by Steven Moffat does do a fair job of balancing horror and comedy and most of the jokes are quite funny.
* Director Paul Wilmhurst does a fantastic job of pacing the horror elements of this episode and choosing just the right angles at which to film everything.
* Hats off to the production team for designing a motion-picture quality beasty with the Dream Crabs.
* As usual, Peter Capaldi and Jenna Coleman give a merely decent script far better treatment than it deserves.
* Nick Frost steals the show as Santa Claus.
* Albert Einstein once said "The secret to creativity is knowing how to hide your sources." By that definition, Steven Moffat is one of the least creative writers ever. Bad enough that the script name-drops Alien. Worse that it has a literal check list of movies that clearly inspired the episode (Inception, The Thing, etc.).
* The episode also "borrows" a lot from earlier New Who episodes and Moffat's old scripts in particular. Santa's dismissal of the infected crew is exactly the same as The Doctor's dealing with the victims of The Empty Child in The Doctor Dances. And the Dream Crabs are virtually the same monster as the beetles from Turn Left.
* While the Dream Crabs are well-designed monsters, surely a better name could have been provided for them?
* Like The Return of The King, the episode suffers from having a few fake-outs too many regarding the fake endings.
THE FINAL VERDICT
It seems less like a Christmas special and more like a continuation of the last season's more horror-based scripts. Yet it is undoubtedly a Christmas story and it's quite an enjoyable one, in spite of its flaws. Like a stocking filled with candy and one nectarine, there is enough right with this episode to justify the questionable bits.