I think people are way too hard on this episode, sometimes.  David Bradley is charming as hell as the First Doctor, and the jokes are just that.  They're pretty funny to be honest because they aren't too far from the actual writing of the First Doctor at times, too.  I like how the writing makes use of the Christmas Armistice in a big way, too.  That's a nice use of real history to tell and effective story that's pretty rare for the Moffat era.  Plus the way the aliens weren't evil was a fun twist we don't often get to see.  It's a very charming and hopeful story overall, one I quite enjoyed on the whole.  While it definitely gets overblown at times (the speech at the end is way too long for my tastes), I think it's pretty great overall.