The Moscow Option yesterday whilst sat at CDG and have been pondering it since. I didn't think there would be a lot of alternative gaming potential in it, but I was wrong.
(Ok, there are spoilers ahead if you are going to read the book, so stop now).
The alternate 1941 offers little, the battles being extensions of what happened historically, 1942 though is a different matter...
Whilst the invasion of Malta may have little different to that of Crete, other than the opposed Italian beach landings, the fall of Egypt has some limited involvement of a rebellious Egyptian army and the battles in Palestine have some fascinating actions between the Germans and a combined Anglo-American army. The fall of the Cacasus to the Germans leads to a German invasion of Iraq and Iran, with Soviet units fighting alongside the British, whilst in the Far East, the Japanese army gets a bloody nose when it invades Siberia.
All these scenarios are easy to play out using mid-war kit, but will give you a realistic background to what you are doing if you fancy. A really good book, it is a shame Downing did not write the sequel, especially as him tantalisingly mentions a German Civil War between the SS and the Heer at the end!