Eastern Front
Buy this firstRedditors who own the full set name Eastern or Mediterranean as the first army pack to buy, and say the theaters give the most extra 2-player scenarios for the money.
Needs: Just the base game
Adds: Soviet army pack: 42 infantry, 24 T-34 tanks, 6 ZIS-3 guns, 44 mostly winter terrain tiles, badges and 8 new scenarios.
Fixes: Opens up Eastern Front battles and a second army to play, so a pair who has played the base scenarios often gets fresh, different-feeling fights.