As of when this will be posted Gintama hasn't any Christmas episode for this year yet, however, it has provided its fair share of Christmas episodes as it went on for 4 years before re-starting earlier in 2011.
In the beginning of 2011, when I heard it would come back after a few years hiatus, I hurried to catch up on the 150 episodes I had to catch up on. Gintama is special to me, Gintama is one of the first anime I have downloaded back in the days it was only 100 episodes long, for some reasons (read : the team translated from English subtitles to French and it was just bad translation) I stopped watching halfway, always telling myself I'll continue at some point. (Read : when my English level would be sufficient to accurately follow the jokes. Now I can even somehow, maybe, follow some of them in Japanese, it was about time I pick it up again)
And thus I finished the first season before the start of the second. And, so far, that second season hasn't disappointed the slightest bit.
All I can say now is that I'm eagerly waiting for Gintama's Christmas episode, as it is always hilarious. And I'm recommending it to you. While the jokes may be sometimes trash, while the tone might sometimes be serious, a friend of mine told me she wanted to become like Gin and I think there are much worse heroes than him in the world.
Children, don't celebrate Christmas that way at home though!