What's the difference between normal and Christmas beer? What makes them special?
A Christmas Ale seems to be another term for a "Winter Warmer" beer -- a dark, malty beer (raisins, dark fruit) meant to be enjoyed in colder months, with a warming effect, either from the actual alcohol, or spices it was brewed with (think nutmeg, clove, that sort of thing). To my mind, its kindred to a barley wine, just spiced up. This is not a warm summer day, sitting on the porch, type of beer, as you may have guessed.
So a Christmas Ale is a sub-classification of beers in general.
What's the difference between normal and Christmas beer?
Beer may be beer to most people, but in Norway the Christmas beer par excellent is the juleøl:
The drink par excellence is the juleøl, the Christmas beer. It is a sweeter than usual beer that norwegians usually drink at Christmas and that is supposed to be good with the big meals. The other traditional drink at this time of the year is the gløgg, mulled wine with spices that people have with almonds and raisins. - The tradition of Julebord in Norway
Christmas beer are seasonal beers brewed for consumption during Christmas period. These beers often (but not always) contain more alcohol than the brewery's other types of beer and may also contain spicing. It is usually quite dark, but not as dark as a stout, with a big malt presence.