With this Christmas episode Glee presents the first example for this season of the dreaded "special theme episodes" that were the scourge of the 2nd season. And the writers have demonstrated that they didn't learn too much from last year's faults.
Mind you: there are cute moments. The whole 50s-style black-and-white part -the core of the episode and in all evidence the section the authors bet on to make the episode interesting - is fun to watch. Some cheesiness is to be expected in a Chrismas episode (even if we are at the limits here). The choice of songs is not spectacular but ok (but why does Rory only sing slow/sad songs??).
Pity, then, that the script is a disaster at many levels. First of all, every plot in the story is completely uninteresting verging on the irritating (Rachel and Finn's Christmas list? really??). The introduction of Star Wars (a wasted franchise here) was not just nonsense, which can be accepted, but not even funny.
Then, the writers resorted again to the hateful habit to give a 180 turn to the characters out of the blue. Guys, if you want to make Sue become a complex, tridimensional character you should try harder than throwing her as the supreme villain one episode and Mother Teresa the following one. And of course it's completely normal that Kurt is nicely listening to her after her smear campaign towards his father... and so on.
In conclusion, unless you learn how to make special episodes, dear Murphy & co., please no more!