Goodgulf:
To have any hope of success the German player has to start building ships from the start (most capital ships taking 2 years to finish), focus on Naval Air (with long range fighters to protect those planes), and achieve total air superiority any area where he wants to land troops. And as this "West First" gamble is happening, the Soviet slowly builds up - maybe getting to the point where they can go adventuring in the middle east (Persia, Iraq) or in the north (Baltic and Finland) - or conserving their strenght for an invasion west.
Historically, the British left their equipment on the beaches of France - but that equipment could be replaced easier that the men who were saved. After river boats were used to pluck British troops from the French beaches Hilter moved river barges from Germany to France in anticipation of being able to use them - where most of them eventually rotted.
Looking at WWII (or any war) brings amazement at how close things came to turning out differently. Every battle has countless "if only"s as do all the fronts.
And yes, about 90% of the dying happened on the Eastern Front.
Well, the Germans couldn't have forced a classic cross-channel invasion without dominance of the air, but I have read accounts speculating that an improvised paratrooper invasion, no later later than early July, could've given them control of southern England before the British Expeditionary Force could've been effectively rearmed.
General Karl Student, Germany's leading paratrooper commander, proposed such an option to Adolf Hitler--but again, political considerations (the same ones that influenced the decision not to attack the B.E.F. on the beaches of Dunkirk) appear to have been paramount in Hitler's decision-making. He felt that, threatened by German air power, facing a U-boat blockade and standing without formal allies, the British government would make peace with him; AFAIK he never took invading Great Britain seriously, it was all bluff and bluster on his part.
Student's proposal was certainly risky, but I've read historical analyses that consider it plausible given the high competence and fighting spirit of the Wehrmacht at the time and the B.E.F.'s momentary disorganization and lack of heavy weaponry. Reinforcements and some material support could've been flown into southern England by the Luftwaffe assuming that German paratroopers could've captured a couple large airfields; sending in troops and heavy equpment by sea would only have been possible if/when the Germans controlled the shore batteries on both sides of the English Channel.
Of course, it would've been much simpler for the German panzers to have overrun the British forces on the beaches of Dunkirk in mid-June of 1940--but IMHO Hitler never truly desired a German conquest of Great Britain, he wanted an alliance (or at least an understanding of friendly neutrality) instead... --C.K.