Totally awesome and hard maps pre-Hell Revealed era.
The maps are good with some christmas themed stuffs, like snow and some new music, and the awesome status bar with santa claus. But its no more than that.
If you really want to play this to its full, i recommend you to search for the h2h-xmas-fix.wad that @NightFright made. It adds a fix for map14, some new graphics, and most importat, it adds a proper dehacked patch with some neat text screens and maps names.
If this is not enough and you want the ultimate christmas experience, Doomxmas is the answer: it adds properly themed mosters, iced doom textures that greatly enhances the look of the maps, new christmas themed weapons, new sounds, and a dehacked patch for some neat tricks with the mosnters. And also it comes with a neat music pack with a ton of christmas songs to wisthle along!