Battle of the Bulge is a Mod focusing exclusively on the battles in Belgium and Luxemburg, December 44 - January 45.

It converts the Summer/Normandy Scenario of CoH into a winter scenario along with winter Maps, Skins and units.

Lots of emphasize has been laid on the look of the Mod. All skins are as accurate as possible, from uniform detail to unit marking. EACH soldier in a squad has individual uniforms and equipment.
Occlusion effects, team colors, even territory borders and selection markers have been removed for visual authenticity.

Furthermore, the Mod's aim is to combine CoH game play with more realism and it tries to reflect the battle properly. Therefore Panzerelite and Brits have been taken off the game ( Brits will show up as doctrine reinforcements, though ).
You can call in battlegroups which have originally taken part, like the 14th Cavalry Group or the infamous Kampfgruppe Peiper.
Tons of changes have also been done to unit stats, gameplay and doctrines. The units you can produce depend on the doctrine you choose.