I felt that Dom II didn't have too steep a curve, but the interface was not what one would call initially intuitive. I was lucky enough to find Bruce's walkthrough while trying out the demo so I never had to go an extended period of time without knowing what was going on, but I definitely had to help my friends out with some very basic army commands in the game -- part of that was definitely the manual, as it was mostly text and didn't give you diagrammed game screens or a tutorial to get you started.
As for learning the strategy of the game itself, that can be pretty steep. The game is incredibly deep with a wealth of options -- it takes time to learn how one nation matches up against another, to say nothing of all 18. But half the fun is trying, failing, and learning.
