Gary, I too have been working on a European theater of war scenario for some time now, and have seen a few things with the AI:
1) the longer you play, the AI has a tendency to overbuild units and underbuild supply. What I do is assign the AI regimes with some extra HQs and pile on the supply points. Think of these as "supply depots".
2) AI has been rather weak at defending major cities. You can create an event: if a German unit crosses or lands on a pre-defined hex (say, a two hex border around Paris), then an event is triggered that places extra "garrison" units in that city. I usually add 50-100 infantry + some anti-tank & machine guns. You can define them in the units menu in th editor.
3) another challenge will be that all the nations will be unrealistically agressive, with everybody declaring war very early in the game. You can adjust the AI agressiveness in the settings menu. You can also define some of the nations as "sleeping", then create an event that wakes them up - be it a hex becomes occupied by a certain regime, or simply "turn 9, Russia awakens.
The good news is that although it takes considerably more time, you can create a game with an AI that is at least as good as the random game, and via a few events (ie. "cheats"), make the AI better than random game AI. (still not a compelling as a human opponent, but fun for solitaire play, which I enjoy too)
good luck --