Unfortunately this supposedly realistic game doesn't seem to be win-able as the German player in Campaign Mode playing against Poland (Case White) UNLESS you turn off Fog Of War. With Fog Of War turned on, the "German" almost always overestimate the strength of Polish units to the extent that they think they see 7,500 man Infantry Divisions. I don't have the exact figures in front of me, but I know the Polish did not have such grossly over-strength units. Or is that just the Fog Of War over-estimating strength? Either way, whether the units is over-sized or the German recon is guessing wrong, it wastes game turns trying to figure out how/when to attack it. Because you just can't leave a unit of that large size in your rear. What I'm describing is true even on the so-called "easy" historical setting. The German player needs more time. I have played several times and lost by 5 points. There simply isn't enough time to accomplish what the Germans actually accomplished therefore making it Allied biased. THe last Polish resistance ended around October 12th. So the player should at least have until the first week of October. (Even if it took until December, it would not have effected the invasion of France.) So 3 things:
1) Not enough time. (Where's the game editor so we can add a few turns to the scenario without redesigning the whole thing from scratch?)
The game engine and A.I. also play the Polish much tougher and smarter than the Polish actually behaved in real life. Thus making it take longer.
2.) The German armoured and motorized units were much more effective in real life than in the game. They are also too slow and need more movement points per turn. Each turn is 2 days not 1 day. But the amount that they can move in a turn looks more like 1 days movement. Surrounded units should not take 2-3 turns to destroy. In a 2 day per turn game, they should be destroyed no later than the 2nd turn of encirclement. I could see it taking several turns if each turn were a day. Because of the movement point lack, surrounding units takes longer than it should. The German units seem to be too weak (or POles too strong) and are forced to over-stack thus suffering more losses and leaving some ground open and unprotected. Surrounding and air support need to be more effective as they were in real life. Is supply considered when surrounded? Lower morale? Lack of supply and weakened defense should go into effect immediately in a 2 day/per turn game. Also, when a unit is surrounded, the attacker should not have to keep a unit in each surrounding hex. Merely driving over ground changing the map color to "occupied territory" should be sufficient to accomplish encircled status and reduce morale and supply.
3.) Some of the POlish units appear to be way too strong (maybe due to fog of war over-estimating?). Even if a Polish unit had 7500 men compared to a German unit that has 4,000 men, the smaller German unit was more powerful and efficient in it's use than the Polish unit. No Polish unit should be more powerful than the same type German unit (combat-wise not manpower wise). Regardless of the head-count. Polish Infantry Divisions 1-4 were Guards units, elite, and were equal to the Germans in strength and effectiveness. In other wargames of similar design and scale, the unit would be a 7-6. 7 attack/defense, 6 movement. The other Polish Divisions would be 6-6, 5-6-6, and 5-6. The Polish Reserve Divisions would be 4-5-6, 4-6, 3-4-6, and even 3-6. Some slower units would even be 4-5, and 4-4. Most Polish Infantry were weaker in attack then defense. So counter attacks were infrequent except for Warta and Bzura counter attacks. (A fun thing for the Polish player to do is take their many heavy Cavalry Brigades and "invade" East Prussia with their higher movement halting German attacks from the North and only fighting against weaker German garrison troops and security forces.)
I tell you this as a published wargame designer/researcher myself. I feel that a better representation of this topic is John Tiller's "The First Blitzkrieg: Total War In Europe" Campaign series from HPS Simulations. It also contains an excellent editor which can be used to build a game/scenario from scratch or to edit existing scenarios to tweak them.