Mr. Monk and the Secret Santa is the perfect holiday episode. It is not too corny, but also has the right amount of holiday cheer. There was quite a lot of character development here also, particularly with Captain Stottlemeyer. However, the episode isn't too heavy on drama, and I found it to be one of the funniest of the season. I especially enjoyed the hilarious duet with Stottlemeyer and Randy, and the Monk as Santa scene. Those were both gems.
That being said, the episode was not perfect. The Captain's encounter with the nun seemed a little forced, as if the writers had to put something religious in there. Also, the mystery was pretty weak. But these are just minor flaws in a great episode. So grab a cup of hot chocolate and enjoy this delightful Christmas special.