Overall, Imperial Glory was indeed a failure
Units moving at incredible speed, melee fights to the death without any possibility to withdraw.
But it did some things right, especially in campaign mode. Multinational armies, peaceful annexations, embassies, victory objectives on the battlefield...
I find the Embassy idea especially interesting. ETW won't allow building anything in another nation's territory however. But there may be aworkaround using character traits and agents. For example, have a trait "Ambassador" for gentlemen, so when you put him in another nation's capital it increases their opinion of you. As a bonus, this would make these agents actually useful (though I doubt the AI will be able to take advantage of this).
As for multinational armies... I refer to
The Rights of Man mod for ETW (shameless plug
)